"I was diagnosed with walking pneumonia earlier today [Sunday], but I was determined to give you the best show humanly possible," he said in an Instagram post after the concert. "I played and sang my heart out until my voice could sing no more."
Walking pneumonia is an infection caused by bacteria that mostly affects people's respiratory tracts. It's less severe than other forms of pneumonia but can still leave people feeling sick.
Despite efforts to battle through his set, he was forced to cut the show short.