He didn’t “collapse” or “fall”. He reached for his ear (where he was hit) and had a general “WTF is going on” face, then after a few seconds, ducked behind the podium as secret service yelled at him to get down.
He seemed able to walk away on his own, although it is hard to tell exactly since his human shields might have been supporting him. As he was leaving, he was well enough to project an image of good spirits and raise a fist, seemingly getting into a bit of a fight with his secret service, who seemed to want him to stay small and hidden behind them.