Why does this happen when I don't get enough sleep?

I'm healthy little 14 year-old. I eat [fairly] decent food and in general, I take good care of myself. I've noticed that when I don't get a lot of sleep, I get a stomach ache the entire next day. Sometimes cramps and chest pain, too. It's usually pretty distracting. I come home from school if it's really bad. But I typically get enough sleep so I haven't really addressed this problem. Anyway. I stayed up til about 1 last night, then remembered I had to get up at 7. So I got a good 5 and a half to 6 hours of sleep. I was also very stressed (it was a driving test) so it wasn't even decent sleep. So I've had this killer stomach ache and diharrea today (embarrassing...). So I guess I'm wondering why this happens and if I should worry about it. Any ideas?