Why does my femur head pop out of my pelvic joint when I lift my leg up?

When i lift my left leg up or when i do bicycle kicks, my left femur head pops out of my pelvic joint. It doesn't hurt when it happens, but i don't think it's suppose to pop out. Is this really serious or can just rest and let it heal on it's own. Also it's been like 1 week so far.