Speaking after Ryan Jones revealed he has been diagnosed with early onset dementia, Marler, 32, called the former Wales captain's diagnosis "awful".
The 83-cap England man recalled a "big blow" in a match that knocked him out.
"I was out cold and I remember being in the physio room next and the kit-man came in. I just broke down and I had no recollection of having kids," he said.
Speaking to TalkSport, Marler added: "It just really scared the life out of me."
Harlequins veteran Marler was knocked unconscious by England team-mate Billy Vunipola's hip during his side's Premiership win over Saracens in September 2016.
Jones was told he had a severe case of probable chronic traumatic encephalopathy (CTE) in December 2021 and has joined a legal action, led by figures including England World Cup winner Steve Thompson and former Wales international Alix Popham, against rugby union's governing bodies.
Three-time Six Nations winner Marler said his wife has urged him to follow concussion protocols, adding: "It's awful for Ryan to be told that and be going through that.
"I've just buried my head in the sand, to be honest, because it scares me. I just ignore it and bury my head in the sand.
"But the more it comes out and the more apparent it becomes in the sport, the more boys are getting diagnosed with this stuff. It's sad.
"There is always going to be that element of danger and you don't want to remove it so that it isn't rugby anymore.
"But you do want to be well informed going into it. As long as I am informed with what the dangers are, I can make an informed choice."