I always stay up the whole night! Could it affect my health?!
Question: In what way??
Answers: In what way??
It will affect your immune system; impair your response time (IE: for driving); impair your judgment; concentration; attention span; memory; strain your heart.
EDIT: Sleep deprivation can lower your immune system. Researchers don't know why the body needs to sleep, but when research was done on rats that were deprive of sleep, their immune system was affected where they became ill often, and they eventually died after 2 weeks (scientists kept them from falling asleep).
Not to say you will die, but it will cause you to be terribly unhealthy.