Yikes that would make me nervous too! I have had no direct experience like this but I did hear of a similar experience once from friends of my family that I never fully believed until now haha.... They had a good sized ball python with a great temperament and one day it wrapped one of the girls wrists and tightened like you described, then it bit her slowly and continued to constrict. The family tried pulling it off with no success. Her hand had no circulation so they had to eventually pry his mouth open and ended up breaking his jaw, poor guy. Apparently the snake healed up fine but they gave him away after that. Very strange but apparently not totally uncommon from what you've said