I read this study that you should plan your sleep for 90 minute intervals...you go through an entire cycle in 90 minutes. So its possible for you to wake up after 4.5 hours of sleep and feel refreshed, rather than sleeping for the 5 hours, because you aren't breaking a cycle. I actually tested it a few times and it does work. Granted, the getting up part is the hardest for me regardless if I've had 4.5 hours or 12 hours...I always wake up tired. But after planning the 90 minute thing and sleeping for exactly 6 hours, I felt pretty damn good after I actually got up.
I've been surprised at how rested I felt sometimes when I had to get up after less than 5 hours...couldn't really figure it out. How interesting.
Cherry Pepsi always did it for me, when I needed to stay awake on the job. Sleep,,I went years with sleep deprivation, due to my crazy wife. I ended up with Restless Leg Syndrome, which also deprives one of sleep (it's got it's own Wikipedia site, google it). My solution? Medical Marijuana. All I can say is,,it works for me. Good thing I live in California. But yeah,,a hit, or two or three,,and I'm out. I've even been sitting at the computer, and when it takes effect, I've passed out and hit my head on the monitor. One time, I hit my head on a glass of water sitting on the desk in front of me, and it spilled all over. Just the other night, I even passed out standing up, and almost knocked over a bunch of glassware. Stuff's potent, but effective.
i feel rested when i get up after less than 5 hours too. i'm just ready to pass out 5 hours after waking up in that situation.
I almost never get more than 5-6 hours thanks to a hectic work/school schedule, and during finals, I'm lucky to get 4 hours a night. (Yes I know, more sleep equals healthier lifestyle and generally better grades, but I make it work somehow.) All I know is I am always thrilled when I actually get the rare chance to "sleep in," which to me is like, til 9am.