Why whenever i lay down on my right side, the room spins?!?!?

When i go to bed in the night and lay down(on my right side), my entire room looks and feels like it is spinning back and forth and up and down extremly fast. It is quick, jerky, violent movements and sometimes it gets so bad that i feel like i will fall off my bed or i cant distinguish one object from another becuase they are moving so fast. I do not drink or smoke or anything and this has been happening for about two years. Ive been ignoreing it until now becuase i didnt think it was that serious. I am also very lightheaded when it happens. its wierd....only on my right side.... any idea of what this is?