Dizziness. Headache. That's what 52-year-old Sen. Mark Kirk of Illinois, who filled President Obama's former seat in 2010, complained of when he checked into a Chicago hospital on Jan. 21.
Doctors discovered Kirk had suffered a stroke, caused by a tear in the carotid artery in his neck. Some strokes are caused by bleeding in the brain, but most, like Kirk's, are ischemic -- the result of a blockage halting blood flow to the brain.