The star, real name Terry Brunk, was scheduled to appear at a Extreme Championship Wrestling reunion event and when he failed to show, handlers tracked him down to his hotel.
Sources tell TMZ.com that the fighter had an allergic reaction to a medication he had been taking.
A representative for the event says, "Sabu was found unresponsive in his hotel room... Management is currently awaiting results from his doctors to find out what actually happened.
"All we know is that he had prior health issues that might have been a contributing factor. We're pulling for him and are very concerned for his health. We wish him the best of luck in his recovery."