Why do I have lewd dreams even though I never think about anything of the sort?

Assalam O Alaikum WRWB,

This is something that has been bothering me and I cant make sense of it.

So I know that dreams are the creation of whatever goes through out minds throughout the day and more so what we are thinking about when we are in bed about to sleep. I also understand that some "bad" dreams are from Satan trying to influence us and some come as part of our "hormones".

But I am all past all this (I think). I am far too "old" to have hormones effect me the way they do teens. Take last night for example. Last night, I work up for Tahajjud, offered it, offered Fajar and then went back to sleep. I was doing Tasbeeh when I dozed off. It is then that I had the most horrific lewd dream involving "people" that I can never even imagine.

So the question is, why does it happen? It does happen very frequently but enough to unsettle me.

JazakAllah.