The man really seemed very unstable. There was something wrong with his balance. A normal person would not have fallen like that.
He seemed agitated and uptight, and acting in a rigid manner when he tensed up squaring himself up to the police in a semi aggressive manner- - this can sometimes affect balance as the body is ‘bracing itself’ the muscles can get rigid- kinda like when a person is shocked by seeing something that makes them tense up- - but he was older- maybe there was a condition he had besides- don’t know- hard telling from the video
He mighta been a bit mentally unstable- seems he was pretty agitated-