I've think I've heard this called an autistic 'special interest' before but I think that sounds a bit condescending- I dont know what else to call it though!
I get a obsessed with things from time to time- without being too specific, I have a rough rotation of particular games, hobbies and books that can become all I want to do.
I don't always have one of these focuses on the go, and when I do It doesn't go so far as to impact my daily functioning- I can still work/ parent/ chores etc. But I will happily lose sleep to peruse these interests in my down time, and sacrifice social opportunities.
I rarely talk about these interests as I'm aware it's probably a bit odd, which is probably why I'm posting about it really. Does anyone else have this, and what's it like for you?