is it bad to stay up all night?

There are people who lives the "night" life. Graveyard shift people and stuff. Staying up late is alright as long as you manage to get the right amount of sleep. If you are like sleeping 3 hours a day then no its god damn unhealthy and you probably will act like a zombie. However if you have the luxury to sleep a good 7 hours and stay up late, you should have no problem.