Droopy door syndrome

My driver's door has drooped a little recently and is hitting the catch pin, also the bottom of the door card rubs on the way out, she's going in for a service soon so I'll get it looked at then but I was wondering how many others have had the same experience and what the common causes are? The hinge seems pretty solid with no movement in it so I'm a bit baffled, needless to say the passenger side is perfect.