David Hasselhoff has fallen off the wagon in a big way, at pal Simon Cowell's big birthday bash in London.

The Sun reports that the Baywatch star got so out of control after drinking for days (starting with Cowell's party last weekend and continuing at London's St. Martin Lane Hotel), that his assistant had to call in a doctor to deal with the belligerent star. But David was none too happy about this latest intervention and lashed out, accidentally punching the doc in the face.

A source tells the paper, A source close to the star said: "David is very hard to handle when he drinks, often very emotional and aggressive. On this occasion he became so drunk he wet his hotel bed - ruining two mattresses - and was becoming a real pain for staff. His assistant Joe Townley was so concerned he called out a doctor. David was furious and lashed out at him - but mistakenly hit the doctor. They decided they had no option but to lock him in the basement until an ambulance arrived."

The Hoff was taken to Capio Nightingale Hospital, spending two nights in a private suite before being discharged yesterday.

Last month, David denied being hospitalized for alcohol poisoning, calling it a bad reaction to medication instead. But it's undeniable that after this incident, the Hoff needs serious help.