We have all had times in our lives where we cannot avoid going without sleep. Here is a little trick to dealing with early morning classes or meetings alertly after only four hours of sleep.
One half-hour before going to bed (you've finished your studying and just need to print it out and get ready for morning) have a small glass of Coke. This might seem insane, but the truth about caffeine is that it takes three hours to hit your system.
The initial buzz you get is a overlay of a sugar high with the temporary alleviation of caffeine withdrawal symptoms, both of which will leave you crashing to a low and instant sleep as soon as your head hits the pillow, especially if you have an unfocussed background noise source running.
Now while you sleep that caffeine will process and one hour before you wake your system will perk up. So when your alarm goes at that ungodly hour, you will find yourself oddly alert.
Don't forget to take another hit before you leave the house, because the effects will fade after a few hours.
And remember, this is only a cheat - you will get very tired in the afternoon, and it's not the best thing to do to your system regularly.
But at a pinch, it works.