Poison front man Bret Michaels is in critical condition following a severe brain injury, though little else has been released regarding the exact condition of the singer and reality TV star. Michaels was rushed to the hospital last Thursday and is undergoing multiple tests after suffering an intense headache, which some think may have been caused by a subarachnoid hemorrhage.

Such a hemorrhage is usually the result of a brain aneurysm, which can go undetected for years before appearing violently and seemingly out of nowhere. While millions of Americans walk around with brain aneurysms every day, according to Mayo Clinic, only a handful of these actually begin to bleed.