DS1 is a sensitive soul and gets very upset when he bumps into things or is touched by a stranger. Eg today he accidentally bumped heads (not that hard) with another boy at the playground and screamed (really screamed) then whacked himself in the face several times. Later, a woman at the cafe ruffled his hair so he hit himself on the head. At bedtime, he bumped his head on his chest of drawers, so headbutted the (thankfully carpeted) floor!
It's really upsetting to see, is it normal? And how can I help him stop?