Paul O'Connell made his Ireland debut against Wales in 2002, though he doesn't remember much of it.
Not long into the game, O'Connell was knocked unconscious by an elbow from Craig Quinnell. He played on and scored a try though he has no memory of doing so. Under protest, he was replaced just before half-time.
Former Kilkenny hurler DJ Carey has a similarly alarming story of his experience with concussion.
Speaking on Newstalk's Colette Fitzpatrick Show, Carey said that he suffered seven concussions in his hurling career though he does not remember all of them.
One, in particular, does stand out for the five-time All-Ireland winner. During a game for Young Irelands in 1992, Carey took an elbow to the head. He played on, though later in the game, the effects of blow began to tell.
One - not that I can remember it - I can remember being told about it. I got an elbow I think in a county final in 1992. Now it was accidental and I went down, and was down for a couple of minutes but I played on for almost the whole game.
I went in at half-time; played on in the second half. We got a free with about five minutes to go - it was important, seemingly; straight in front of the goal and I aimed for the corner flag.
Then someone thought there was something wrong with me and I was taken off because obviously, I wasn't playing well.
After being substituted, Carey lay in the dressing room, possibly on a stretcher, though he cannot be sure.
Kilkenny manager at the time Ollie Walsh came in to check on Carey. He has no memory of the conversation.
My Kilkenny manager at the time - this game was with my club - was Ollie Walsh. Ollie came into the dressing room afterwards and I was on a stretcher. He said something and I said 'That's grand Ollie, I'm going back on in a few minutes.' He said 'Grand Carey, but I'll hit the frees.' Now Ollie was 65 or 70, he was gone from hurling but he was manager of Kilkenny.
So we had a full conversation but I have no recollection to this day.
You can listen to DJ Carey on The Colette Fitzpatrick Show below.
Picture credit; Ray McManus / SPORTSFILE
READ HERE: DJ Carey Explains Why He Retired For Six Weeks In 1998
