The condition, called hyponatremia, is a side effect of a brain hemorrhage that has left the Poison frontman in intensive care at an undisclosed hospital.
The tests also found the 47-year-old Michaels suffered a type of stroke that causes bleeding in the fluid-filled spaces around the base of the brain.
Michaels' New York-based publicist Joann Mignano provided a written statement confirming the Web posting.
The message said doctors are hopeful Michaels will gradually improve as the blood surrounding the brain dissolves and is reabsorbed into his system.
