I can remember one night when I only slept about 90 minutes, the night after I ended up being so tired that I fell asleep at 8 PM, slept until 10 PM then stayed up for a little while and ended up falling back asleep around 11:30 PM or, after that I pretty much slept non-stop until about 10 AM, but I think that all of this was because I was completely exhausted and was trying to catch up on sleep.