From The Olde Disc Jockey's Almanac this morning, 35 years ago today was a bad one for Keith Moon and the Who...
"March 9, 1976…For the second time, the Who's Keith Moon collapsed while performing at a show, this time at Boston Garden. Though drug and alcohol abuse were again the culprits, singer Roger Daltrey told the crowd that Moon was suffering from the flu. The performance ended at that point but the group played a make-good concert for ticketholders on April 1."
Here's a video of another time he passed out on stage. You can see Roger and Pete discussing what to do, and Roger saying "He's out cold." Then you see Keith actually being carried off the stage. It's a pretty compelling video.