You know what, I've never really looked into what that "condition" is called. Quick Google search and it turns out it's called "orthostatic hypotension (postural hypotension)." It's a form of low blood pressure caused when standing up too fast after sitting or laying down for a long period of time, and it's often the result of being mildly dehydrated, low blood sugar, or being too hot. It's really only a worry if it happens extremely often and/or causes more concerning issues like blacking out and fainting.

Yah this used to happen to me too. One time it was go bad I was blind for like a full minute. Needless to say I didn't go to school that day.