I've got Non 24 / Free Running Disorder, so my sleep cycle is basically longer than 24 hours.
Every solar day I'll wake up and go to sleep around an hour later than the previous one, so in about a month I'll cycle right round from a roughly normal sleep pattern, to being nocturnal, and then back to normal.
Before I ended up isolating myself following a major bout of depression, I'd pretty much just lose sleep trying to be awake during the day, and spend nights just lying in bed staring at the ceiling, utterly exhaused, but unable to sleep. When I did finally get to sleep at a time my body wanted, I'd regularly sleep for 16 hours or more, just to catch up on all the sleep I'd lost. On several occasions I've woken up a day later than I expected to.
After a couple of solid months without any interruptions from other people and obligations, my body got the chance to fall into a pattern that it considers normal, and I was finally getting regular healthy amounts of sleep, even if they weren't at times that anyone else would consider normal.
I researched sleep disorders beyond simple insomnia, went to my doctor asking for a refferal to a sleep specialist, saying what thought the problem was, underwent a 3 week sleep study, and was given the diagnosis.
In sighted people it's apparently genetic, or due to damage to the parts of the brain that govern circadian rythms, and there is no real treatment. You can be given massive doses of melatonin to force your body into a regular pattern, but you build up a tolerance so it's effectiveness is very limited.
My social life just doesn't exist, because I can't make plans more than a few days in advance, because I have no idea what my sleep pattern will be like, thanks to how any interferrence with it from appointments, visitors, or just phonecalls at the wrong time, can throw it off, with it taking several days to settle back into a regular pattern.
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