This has run in my entire family and happened to my grandparents. I sleep for about 2-3 hours at a time, with or without sleep meds. like ambien.

Sometimes I can go about 36 hours without sleep, but stilll only sleep about 3-4 hours before waking and then unable to sleep again for several hours.

This, obviously causes my to have to sleep in the afternoon for a couple of hours and then I'm up all night again.