OP I have been in a similar situation, it was over 15 years ago and I still think about it sometimes.
I was out with friends and got far too drunk, I woke up in bed the next morning and had no idea how I got home, there was an empty bottle of wine and two glasses on the table, CDs everywhere, my front door was unlocked and I had text messages from a man called “Geoff” saying he hoped I wasn’t too hungover.
My friends said I had just disappeared from the nightclub we were in, apparently I’d been drunk when they last saw me but they didn’t think I was incapable of looking after myself, I’d no idea how or when I got home. I also lost my keys so that added to the beer fear as I’d obviously gone home with someone.
I did manage to contact Geoff who told me that he’d got me a taxi home, drank some wine then I’d gone and got into bed. He said he stayed the night sleeping on the bed covers next to me. Apparently this was because he couldn’t get a taxi to his house that late (small town) and to check I wasn’t sick as I’d apparently been sick previously, he’d then walked 3 miles home to get ready for work in the afternoon.
I woke up fully dressed in the same clothes I’d been out in, there was no evidence whatsoever that I’d had sex and Geoff seemed a genuinely nice man who had wanted to get me home safely and then make sure I didn’t choke on my own vomit! There didn’t appear to be anything sinister but there COULD have been and not knowing or remembering meant I’d never know what actually happened and that terrified me.
I was like you, I went through different scenarios and felt like my brain was blocking something from me or I worried over and over about what could have happened, I understand how easy it is to keep focusing on it because you desperately want answers. I was also fretting about my missing keys, I wondered if Geoff had taken them to start with but it turned out I didn’t have them when I’d got home and had to get my neighbour to let me in with my spare set he had. When I later asked my neighbour how I seemed he just said “pissed, loud and annoying”.
I was a bit wild when I was younger but that night changed everything for me, I didn’t stop drinking altogether but that was the last time I ever put myself in a risky situation. I was single but if it had happened whilst I was married I’d have felt a lot worse.
I agree with the majority of people who think you fell asleep on the toilet. As a pp said the loss of memory is because your brain stops making memories due to alcohol, you would have still been you and if you would never cheat sober then it’s unlikely you did on this occasion, piles are likely from sitting on a toilet seat for hours!
It sounds like you are happy and settled in life but haven’t always had it easy, you have a lot to lose that you value so that’s why you are fixating on worst case scenarios, there is nothing to suggest that you’ve had sex or been sexually assaulted, there would be evidence from both, I’m sure your work mates would have picked up on it too.
It’s either this or you do know deep down but don’t want to face up to it, I think if that’s the case you aren’t disclosing everything because there is nothing in your OP to really suggest anything untoward happened. If that’s the case then you can choose to be honest and face up to it or you can just put that night behind you as a lesson, we all fuck up and I doubt you’ll ever be in this situation again.
Take a pregnancy test and have STI tests if you think they will put your mind at rest, please try to move on afterwards. You drank too much, that’s something that many many people have done before at least once in their life, would you judge them the way you are judging yourself right now? If someone else had posted similar would you think they deserved to leave their husband or would you be sympathetic and assume they just drank too much and likely ended up having a little snooze somewhere?
Please don’t let this keep haunting you, you can’t change anything now and you need to make peace with that, it will take time but eventually you’ll stop thinking about it and worrying and feeling that sense of panic, in a few months hopefully it’ll be just a vague sense of curiosity. I do occasionally still think about “the night of Geoff” as I think of it but it’s more of wondering where the door keys could have ended up or whatever happened to Geoff!