07/31/2009 AT 02:15 PM EDT
Why is Robin Williams planning to return to the stand-up circuit just seven months after having heart surgery?
"I realized I was running out of merchandising money from Bicentennial Man," he joked at the Television Critics' Association panel in Pasadena, Calif. Thursday.
Williams, 58, says his 20-date tour, Weapons of Mass
Destruction, which kicks off in September and which will air on HBO, uses material drawing from "a relapse, three years of heavy drinking, going to rehab in wine country to keep my options open, coming out of that, divorce, and open heart surgery."
The characteristically light-hearted comic admitted that he worried about touring. "After having open heart surgery, it's going to be interesting," he says. "I haven't done the long program [yet]. I started a little bit; I went on stage two
months ago and I was on a couple minutes and then I said, 'I'm not ready yet, thank you.' "
Despite the career setbacks, Williams says surviving surgery has had positive effects in his personal life. "You literally are opened up, and you really do appreciate the simplest things like breath, and friends," he says. "I've been calling up all of my friends and saying, 'Thanks for being there.' You say, take it a little slower. That's been amazing."