He has you covered
The shrinks call it "rumination." Or sometimes "perseverating." It's the habit OCDers (and others) have of "chewing on" things- going over and over them, examining them from all sides, assessing and re-assessing them.
Thinking is a good thing. But we can overdo it. People with OCD often overdo it. That's where the "obsessive" in Obsessive Compulsive Disorder comes in. To "obsess" is to become preoccupied with something, to be so concerned with it that it not only crowds out other things we need to be thinking about but dominates and controls us. For the scrupulous, it can be a question about whether or not something is a sin. Or it can be a theological matter. When that alarm in our brains that goes off at random and so easily gets stuck in the "on" position blares in our brains, we can wind up going over and over and over almost anything endlessly, and without any positive result. We worry ourselves sick. We pour over sites on the Internet looking for answers we don't really need, and which sometimes are known only to God Himself. A random thought becomes a false emergency. A false emergency becomes a needless worry. A worry becomes an obsession, and we become consumed by something we can't figure out and really don't need to.
If you're concerned with whether something you've done is a sin or not, ask yourself why it matters. Contrary to what many people with OCD think, you don't have to confess every single sin you commit. That's impossible. We commit sins we don't even know about. And while the instinct to confess is natural for somebody who loves God, God already knows about our sins, even the ones we are unaware of.
Are you afraid that you haven't repented? Well, the Greek word for "repentance-" the word the New Testament uses- simply means "thinking again" or "changing your mind." It isn't feeling bad or being miserable about something. It isn't promising that we won't do it again- although it probably means sort of not wanting to do it again in the half-baked way we who are sinners, as well as saints, want to avoid sin. It means that the saint in you doesn't want to do it again. But the sinner in you very well may. No, repentance is merely turning back to God. Your baptism is the promise that He'll be there when you do.
Repentance and confession are not really even things we will ourselves to do. They're things the Holy Spirit does in us. They're things which come naturally to a person who loves God and in whose heart the Spirit abides. But wait a moment! There's another thing to obsess about! There's an opportunity to worry that since you don't see a desire in yourself to repent and confess you don't love God! Once you start down that rabbit hole, there's no end to the torment you can put yourself through. And it probably will never even occur to you that if you weren't penitent you wouldn't be worried about not being penitent, or that if you didn't love God you wouldn't be worried about not loving God!
How can a loving God send people to hell? Why does crib death take the lives of babies? Why does cancer exist? There is no end to the ways in which the brokenness which sin has inflicted on the world can bother us so much that we're tempted to blame God for it. Granted that He doesn't cause these things, why doesn't He prevent them? Isn't He all-powerful?
How can God be Three, and yet only One? How can Jesus be both human, and divine? How can the bread we eat and the wine we drink in the Sacrament be at the same time the body and blood of Jesus? The greatest minds of Christian history have wrestled with these matters. Many of them have solutions which can be found, if one looks carefully and systematically enough for them, in the Bible. Others have possible solutions which, while reasonable, we don't know for sure are the actual explanation.
And what about that random thought that just went through your head, that ugly blasphemy or that unspeakable image that just formed in your mind seemingly out of nowhere? That such thoughts go through everyone's mind, and as far as we can tell for no particular reason and certainly no reason that reflects either well or badly on the speaker, is a basic law of psychology. Neurotypical people ignore them so easily and so automatically that they may not even notice them. And here's another basic law of psychology which people who worry about that sort of thing need to keep in mind: the very act of trying to suppress or not think a thought or become upset about it will keep it coming back! The only way to deal with intrusive thoughts is to ignore them for the meaningless nonsense they are. That's what psychology tells us. That's what the great Christians of the ages- people like Luther and Bunyan and Spurgeon- all tell. But when the alarm goes off, and the fear hits, we may forget that.
We don't confess in order to be forgiven. We confess because we are forgiven. Christ promises forgiveness to all who believe. There is no question of our not receiving it, and so we don't hesitate to ask. We confess, too, because when we realize that we have hurt Someone we love it's natural to apologize to that person even though we know that He has already forgiven us, not because we asked and certainly not because we deserve it, but for Jesus's sake!
We repent in the true sense of the word when we want God's forgiveness and turn to him for pardon and healing. And for Jesus' sake, we always receive it- not because we repent or because we confess, but because of Jesus. Even if those ugly and often blasphemous thoughts were sins (which they're not since they happen without our wanting them to happen and have nothing to do with what is in our hearts), we would be forgiven, not because we asked to be, but for Jesus's sake.
There is no need to worry about whether or not something we've done is a sin, or whether we "need" to confess it because God knows whether or not it's a sin, and either way, it just doesn't matter. He has you covered. If it's a sin, He forgives it, not because we've figured out that it's a sin and confessed it but because of Jesus. He does that for all the countless sins we commit every day without realizing it despite the fact that we haven't confessed them or even consciously repented of them. He does it not because we've specifically repented for them or asked Him to forgive them, but because of Jesus.
We are weak. We are sinful. We are broken. But when the Son of God cried out, "It is finished!" on the cross, every sin that would ever be committed by anyone, anywhere ceased in itself to be an issue. It's true that, tragically, the vast majority of the human race will not benefit from that fact, because every relationship has two sides, and if a person refuses to be reconciled to God the fact that God has forgiven them doesn't do them any good. The Fall broke our relationship with God, and any relationship that has been broken will remain broken unless both sides are willing to make peace.
Intentionally pushing away God's forgiveness means that we don't benefit from it. But short of deliberate rebellion, dotting the "i" and crossing the "t" isn't an issue. Its God's grace that justifies through faith, and not even the good work of confessing.
But the mere failure to specifically confess a sin does not prevent God from forgiving it, and the fact that we want His forgiveness and believe that we are forgiven for Jesus's sake is repentance! It's perfectly true that we repent. It certainly is the case that we confess our sins. For that matter, we obey- or try to, even though even our most righteous acts are so ruined by our mixed motives that in themselves they would be sins, if God didn't accept them for Jesus' sake. We- that is, our New Selves-seek to serve God and our neighbor. But the very passage which causes so many scrupulous Christians such fear and agony when only part of it is remembered is transformed from Law into Gospel and from a threat into a comfort when the whole passage is read. Phillippians 2: 12-13 reads,
Therefore, my beloved, as you have always obeyed, so now, not only as in my presence but much more in my absence, work out your own salvation with fear and trembling, for it is God who works in you, both to will and to work for his good pleasure.
We don't so much repent as we are repented. It isn't we, really, who strive to obey God and to serve God and our neighbor. It's Jesus Who does our good works. He just uses our hands and our mouths and our hearts to do them, And He can be trusted to continue to do that until the day we die.
But we can obstruct the process by trying to do the job ourselves. We can make it harder for ourselves and more difficult for Him if our eyes are fixed on our own sinful, fallen selves and on how and what we are doing instead of on what Jesus, Who is always our only Righteousness, has done and contnues to do.
We don't even confess because we are so pious, but because the Holy Spirit fills our hearts with love for God that is naturally concerned if we become aware of having offended him. And God always washes every single sin, known or unknown, confessed or unnoticed or forgotten, whether we realize that it's a sin or not, completely away with the blood of Jesus for anyone and everyone who looks to Jesus for forgiveness and life.
There are many things about God that we can't figure out. Why should that surprise us? God's mind is to our minds as our minds are to those of mere ants. Why should it bother us that there are things our about our loving and gracious Father we don't understand? How could it possibly be otherwise? It's enough that He understands them. It's enough that we know that what He tells us is true, even if we can't see how it can be.
There are many things about our own behavior which puzzle us. Paul observed in Romans 7 that he didn't understand his own actions. But it was enough for Paul that God was in control and had made provision for what he himself didn't understand- a fact which caused Paul to marvel.
There is never a need to obsess. There is never a need to worry. We're OK not figuring everything out, because God has it figured out, and has us covered. "Justification by grace, for Christ's sake, through faith." means that every believer is completely, totally, and absolutely sinless in God's eyes, not because they understand everything about God or confess their sins or because of anything they do, but because of Jesus.
"Repentance" ought to be a comforting word, not a hoop you have to jump through. It should be a reminder that you don't have to jump through any hoops! When you were baptized, you started on a lifelong journey in which sin and unbelief would beset you at every turn. But there at the font, God promised that all you have to do is claim that baptism and your identity as a child of God, turn from what you deserve and claim your identity in Christ- to push the Old Self under the water to drown, bury him, so that a New Self would arise once again, holy and innocent in His eyes.
Repentance is claiming that promise. It's literally nothing else.
"Pray," Martin Luther advised, "and let God worry." There is no need to obsess or ruminate about things God has already taken care of. And God has taken care of everything. He's even taken care of that broken alarm that goes off for no good reason and makes us worry about things He has already taken care of.
Next time that broken alarm goes off, remember your baptism. Remember that it is God Who works within you to will and to do. Remember that there is nothing you need that you will not find by simply looking to Jesus, and resting in Him without worrying or obsessing. And if you find yourself worrying or obsessing anyway, that's OK. Jesus has that covered, too.
Covered in His blood. Covered in His promises. Covered in your baptism- His personal promise to you, whom He called by name, that no matter what you do or don't do, as long as you want His forgiveness and His friendship and the eternal life He bought for you with His own blood, as long as you cling to His promise of an identity as that New Self rather than pushing it away and clinging to the sin and the do-it-yourself "righteousness" of your Old Self, you are righteous and innocent and perfect in His eyes.
And it's all because of Jesus.
So when that alarm bell goes off and that creepy and uncertain feeling comes over you, don't look to whether or not you've sinned. Don't look through whether you've repented. Instead, take the advice of the author of Hebrews, and live your life looking not to yourself, but rather "looking to Jesus, the founder and perfecter of our faith."