When im trying 2 sleep it feels like my body is floating above me n i get a weired felling then it fades?

it only happens when i get into bed and im lying there trying to get to sleep, then it feels like my whole body is slowly floating above me and i get a very weird feeling its hard to explain, it feels like my whole body isn't lying on the bed it last for about 3 or 5 min's then it slowly disappears