Well it still looks to me like he's shifting his weight in the car, when he moves back and forth, and then he got out to try to shake the muscle cramp.
The rest of the video he was walking fine on his own, a little slow (muscle soreness?), but not needing assistance. Hey I'm not sticking up for him, just honestly that's what the car scene looks like to me. Add him being high or drunk to the equation probably making matters worse, but he's not unable to walk or falling down while walking. So could very well be a combo of spasm and drunkenness - the way his foot caved at the end was really weird.