My sleep cycle has been completely whackadoo for over a month now. I have to fight my body to get it to go to sleep. On a good day I'm only up for around 20 hours. A bad "day" can stretch for over 36. And because I have school aged children the amount of sleep I get after one of these spells is completely dependent on factors like day of the week, time my body finally decided to give in, if my mother is feeling generous enough to get the kids off to the bus for me, and a large number of other things that can and do go wrong. Like going to bed at midnight, the puppy waking me up because she's acting like she needs to go out, and then having it turn out she just wanted to chase the damned raccoon. So go to bed at midnight, get up at 3:45, be up for another 20 to "god only knows" hours, and not be able to return to sleep.
And while my therapy has significantly reduced the dosage of anti-depressants I am currently on; most sleep medication, doctor ordered or otc, doesn't mix well with them.