I'm always sleepy and one morning i woke up very dizzy. is this dehydration?

Realize: For a young person, unless you have some significant medical ailments or take medications that really predispose you to significant dehydration, chronic fatigue or sleepiness is unlikely to be the major cause. It can lead to some element of "dizziness", particularly when rising, but again if this is constantly happening, dehydration alone is unlikely the only culprit.