my term-time IS 10 hours a day, it only gets less when im back home for holidays and mother takes it upon herself to wake me up each morning.
Hmmm... That actually sounds like far more than most people get a night! Have you done anything differently over the holidays that might have this effect? The sleeping shouldn't be doing this... Though I'm a humanities student, what do I know?! But on the other hand, at uni I often don't go to bed (I look at it from across the room all night instead while typing frantically) at all, and I'm fine, health-wise...
Look up circadian rhythms (bodyclock). It's an area that isn't that well-known in medicine and there is still plenty of mystery around sleep.
Some biologists don't even actually understand the purpose of sleep because your organism doesn't need sleep to survive in any way. Sure you need rest but that's not entirely the same thing.
There are two phases of sleep: REM (Rapid-eye movement) and non-REM. Apparently, during REM phases, your brain reorganises itself. It's during that phase that you memorise a lot of the stuff you went through the previous day. People who have taken sleeping pills don't have those phases.
I don't know the link between circadian rhythms and the sequence of REM/non-REM phases i.e. the impact that changing your sleeping pattern (as opposed to the length) has on those phases. But there might be a link... It would explain why you feel different to during term-time.
I reckon that lack of sleep ends up having an impact on the nervous system: i.e. your whole sympathetic (fight-or-flight) nervous system goes on overdrive and of course having it in that state too long, must have some sort of long-term effect.
I sleep at 12 am, wake up at 8 am.... and I go to work (summer job). I find that sleeping 8 hours a day is the best, i feel full of energy if I sleep 8 hours a day. Too much/too little, i feel average..