From ages 14-25 I consistently slept anywhere from 4-7 hours a night, the average being about 6 hours. I struggled through high school and university. Towards the end of my University tenure, I finally put serious stock in the old notion that sleep was essential to mental function. After a couple weeks of always getting at least 8hrs/night, I found my memory capabilities (which had always sucked) were vastly improved. So was my ability to focus my full attention. It's now been about 4 years since I started sleeping properly and it's made a big difference. Further, sleep deprivation will cause weight gain has something to do with hormones. My short sleeps wasn't a disorder, I think. Rather, it was lack of satisfaction with the day, I wanted to feel like I lived more, so I'd stay up late reading, programming, playing video games, talking with friends, etc.