Vibrating head dizzyness?

sometimes it feels like a cell phone vibrator goes off in my head, and i get lighthead and dizzy for a few seconds. it happens every maybe once or twice a day. its not painfull or anything its just annoying sometimes, like when im walking or doing a presentation ill suddenly get a vibrating sensation in my head and feel like gravity is pulling me to one side... anyone have any idea what that is?... thanks.