Byran Burrough studies Perry's downfall: 

The most intriguing explanation for Perry’s collapse has been quietly circulating in Austin for weeks. This theory suggests that the governor is suffering from the after­effects of his low-back surgery in July, six weeks before he announced his candidacy; his surgeon, a friend who operates a Houston "medical day spa" specializing in liposuction and laser hair removal, fused two of Perry’s vertebrae and then injected the governor—for the first time in the surgeon’s career—with two teaspoonfuls of stem cells that had previously been cultured from fatty tissue taken from Perry’s hip. 

"Ever since, and you saw this at the very first debate, he just seemed to be very uncomfortable, you know, twisting his torso," observes the dean of Texas political writers, Paul Burka of Texas Monthly. "I think he’s got back pain and may be taking medication for it. He is not on his game. He stopped wearing [his trademark black cowboy] boots and started wearing orthopedic shoes and a back brace. Of course, the campaign denies there is any problem. But he doesn’t seem to have any energy. He just does not look like the same man to me. It’s shocking."