Similar thing happened to me, without the banging though as it was a C172SP... I was still in the learning process, had an instructor beside me and my daughter in the back as she wanted to see what flying a small plane was like. I took off, got to circuit height, started doing some touch and goes and on the second circuit my daughter said:
"Dad, why aren't you wearing your seatbelt?"
The silliest thing about this was that I went through the checklist and checked that the instructor and my daughter were wearing their belts, just forgot about my own....