Former Kansas City Chiefs running back Larry Johnson believes he's living with chronic traumatic encephalopathy (CTE) - the degenerative brain disease found in many ex-football players.
Johnson still holds the record for most carries in a season with 416.
Johnson chronicled several behavioral abnormalities he's experienced over the last number of years to The Washington Post's Kent Babb, which convinced him he has the condition.
CTE can only be diagnosed after death, though researchers are looking for a way to detect it earlier.
In one story, Johnson said he sometimes gets an urge to jump off the rooftop deck of an apartment building. Johnson also said he gets frequent headaches, is triggered by bright lights or noise, and is struggling with a deteriorating memory, among other issues.
Johnson, 38, played eight years in the NFL, most of them for the Chiefs, with whom he was a two-time Pro Bowler. He played his last game in 2011 as a member of the Miami Dolphins.