My little brother always get lightheaded/dizziness (spinning) everytime his head/hair is wet. usually after taking a bath. what might that be?

Vertigo: You describe symptoms of vertigo. This can be from decreased blood flow to the balance center of the brain or to a disorder in the ears. If it is temporary and very directly related to the wet head, it may be a vagal reaction that causes decrease in output of the heart that is temporary and benign. Be sure he lies down, dries off, before getting up and running around. He needs a good checkup.