What is wrong with Richard Simmons?

I am not kidding...what in the world is WRONG with this guy? OK, we all know he is silly, but his appearance on David Letterman tonight was beyond anything I can describe!! Did anyone else see this? I mean, he has to be on drugs, right?! In his 5minute segment, he (while wearing a red feathered tank top and his signature striped shorts) sang ABBA songs from Mamma Mia, bounced around stage and stood on the sofa, and grinned at the camera in a great impression of a manic chipmunk. I honestly think Letterman was a bit frightened...and who could blame him? I mean, Richard Simmons is AWESOME to watch on TV (in a horribly awkward way), but you honestly have to wonder about the kind of people who go on his get-fit self-help cruises...who actually wants to encounter this man in person, much less be stuck on a boat with him for a week?