When i lay down or lie on my sides i feel dizzy, why is that?

Possibly BPPV: If by dizzy you mean that you feel as if you are moving or things around you are moving then that is called vertigo. Vertigo is a problem usually of the inner ear. If vertigo occurs only when you move your head in a certain position and then goes away shortly thereafter it is called benign paroxysmal positional vertigo or "bppv ". This is best treated by an "epley" maneuver.