Kiedis, 53, said a stomach flu and some scar tissue from hernia operation had led to an "impassable inflammation," reported People magazine.
"That becomes an incredibly painful situation where you get a fever and pass out," he said.
His scheduled Los Angeles concert last Saturday was canceled following the hospitalisation.
"We don't really do that [cancel shows]. I'd rather play deathly ill than not play at all, but in this particular instance I was starting to go down, as in to the ground," the musician said.
"I think I had to get sick to take a look at myself and get to the causes and conditions of my overall health," he said. "So it turned out to be a good thing, albeit painful.