Waking from deep sleep

Anyone else baby will be laying down in a deep sleep then soon as you walk out the room boom baby is up. Baby will be laying down in bed like in a deep sleep then soon as I walk out baby is up like how do you go from a deep sleep completely out of it to waking up soon as I leave the room. Especially since it’s not like I was holding baby and r anything I just don’t get it I don’t understand it. Then when I go get try put back to sleep it’s like a while 30 min process which I don’t understand go from deep sleep to don’t want to sleep at all. I’m call the pediatrician tomorrow because I’m completely lost on this one and it’s a nightly thing. Baby will be out at a good time but since I leave the room and have to put back to sleep goes down at a not so good time I just don’t get it