"This [type of hemorrhage] is usually from an aneurysm," Dr. Wendy Wright, an assistant professor of neurology and neurosurgery at Emory University Hospital in Atlanta, told ABCNews.com. "The risk of an aneurysm rupturing is probably related to size -- the larger the aneurysm, the more likely to rupture -- and also may be more likely in people who smoke or on blood thinning medications."
A factor that could have played into Michaels' current condition is his past history of drug use. Michaels hasn't been shy about his hard-partying, rock 'n' roll past. In a 2003 interview with VH1, he described a "menage a mess" from his Poison days, saying, "It was the drugs, the booze, doing the lines off [exotic dancers]."
"Being a drug user, in particular a user of injectable drugs, can damage heart valves and predispose you to get endocarditis," said Dr. Richard Bernstein, a neurologist at Northwestern Memorial Hospital.
Endocarditis involves infection at one of the heart's valves.
Bernstein added: "Cocaine use in and of itself can be a major cause of intracerebral hemorrhage."
ABC News' Dan Childs and Nancy Ayala contributed to this report.