Hank over on vlogbrothers has a quick little video talking about what is arguably a disorder, but only because society doesn’t support it particularly well: having a different sleep pattern than most people.
My natural sleep cycle is the same as his: when left to my own devices, I always tended towards being up til 2 or 3am, and waking up closer to 10am. Of course, for the past several years I’ve had a dog that thinks whenever it gets light out is the right time to wake up, and a job that (when I was living on the west coast) trended towards early morning meetings (to accommodate folks in Europe… and because we just had a lot of morning people on the team). I will say, it’s been a lot easier to wrangle the meetings since moving three time zones eastward.
I’m mostly adjusted to my current cycle (which puts me to bed around midnight and up around 7-7:30), but I still find it pretty easy to start slipping towards 1 or 2am, especially if I’m taken out of my routine for things like vacation. I suspect I’ll still be on this cycle for quite some time, since even if I won the lottery and didn’t need to worry about work schedules, Cecil is still a morning puppy (and Mabel has picked up his habit). And that’s (mostly) fine. But I do sometimes miss the way my brain felt when I was able to be on my natural sleep cycle instead – I feel like I was more relaxed, more at ease, and had more spoons for things.