This article in Abovethelaw.com (quoting the New York Times) says that John Paul Stevens suffered a mini-stroke the day the Citizens United decision was decided by the U.S. Supreme Court, legalizing unlimited campaign contributions and essentially legalizing corporate bribery of politicians.

I found this quote interesting:

his missteps that day led him to seek medical advice and after learning of the stroke, he made the decision to quit. Justice Stevens made the responsible move under the circumstances, because if Citizens United tested his health — and he tells Liptak that he views that opinion along with Heller and the whack-a-doodle reasoning of Bush v. Gore as the three worst mistakes for the Supreme Court in his tenure — one can imagine how he’d have reacted to some of the doozies to come out of the Court since 2010.

I looked up Heller and it was a gun control case.