I think he checked out of the Betty Ford Clinic a few years early. Looking at his eyes in the first part of the video, it looks like there's nothing there.
A Wikipedia entry about him mentioned this which I thought was hilarious:
"In 1994, he was scheduled to perform a concert on pay-per-view from Atlantic City. It was supposed to help reignite his singing career in the United States. On the night of his concert, O.J. Simpson was involved in a police chase on the California highway. People who were watching the concert switched over to watch the news. Since then, Hasselhoff has not attempted another concert."