Ex-NHL star Tim Thomas is explaining why he vanished from the public after his retirement in 2013 ... saying he's been dealing with serious brain damage from a concussion.
45-year-old Thomas -- a 2011 Stanley Cup champ and Boston Bruins legend -- got emotional with reporters before his U.S. Hockey Hall of Fame induction on Thursday ... saying his everyday life was changed after a blow he suffered in his final season.
"I woke up the next morning after it and I couldn't decide what I wanted to eat, where I wanted to go," Thomas explained.