Similar things have occurred with me in the past... albeit not so extreme (or, for that matter, that many times either). Nether-the-less, the reason this happened to me was, quite simply, my lack of sleep. If the body lacks enough sleep, it can enter a sleep that's sufficiently deep that either you sleep enough or it takes some pretty strong stimulus to wake you up. In fact, it can be dangerous to go without so much sleep, since you become more accident prone, have slower reactions and you become generally more irritable.
My advice: sleep more. To do that may or may not be simple, that depends on personal factors, but a few tips on how to do that include:
- Sleeping earlier. This can improve the general quality of your sleep, which can be very important, since some people actually need very little sleep (4-5 hours can be sufficient for some people), but those (few) hours have to count.
- Avoiding drinking stimulants like coffee
- Establishing some pre-sleep routine
- Avoiding stimulus like TV and computer use just before you sleep.
If you suffer from strong insomnia, I would recommend you consult a doctor (something I am not, so take my advice with a pinch of salt), but I would strongly go against using medicine (sleeping pills), not only because of their potential risks, but also because of the dependency they can create. Instead, you should probably try to change your routine so as to improve both the quantity and quality of your sleep.
Of course, considering my own horrible sleeping habits, maybe I shouldn't be giving out so much advice...