Is that common? I would have guessed epilepsy...
It's easy to overheat and fall down.
Even young soldiers in formations on 100 degree afternoons can fall over backwards and as they fall they see the sky apparantly dragging itself to the ground, and then their heads bang the ground and they wake up in the aid tent.
Yup, happens all the time.
I'm hardly an expert but I had a family member that would seizure if they got dehydrated.
They had zillions of tests and everything came up fine, the doctor just said it was congential, no big deal and simply not let them get dehydrated.
He further said that while they looked scary as all get out if and of themselves they weren't dangerous unless you fell or were driving a car.