Recently i keep waking up discovering i cover my whole face with a hand while i'm asleep. i even scared my mother one night when she saw me. i never did this before. any idea what's causing this behaviour?

It is not possible to self asphyxiate while sleeping by putting your hand on your face. The body will naturally trigger muscles to move the hand if the air supply is cut off. As to why you are sleeping with your hand on your face: reaction to items brushing against face, too much light in sleeping room, Air temp too cold/hot, noxious smells, etc.