"A dude knocked me out," he told the Northwest Herald in Illinois, referring to the 2017 season-opener.
"After eight weeks, when I came back, it was constantly on my mind. I wasn't always able to play loose and free. It was in my head. Anytime that's on your mind while you're playing an NFL football game, you're in trouble. You can't play timid. Guys are trying to take your head off, you know?"
Fiedorowicz, a 2014 third-round pick out of Iowa, played in five games last season, catching 14 passes for 127 yards. He was coming off his best season as a pro, with 54 catches for 559 yards and four touchdowns in 2016.
He signed a three-year, $21.5 million contract extension last August.
Fiedorowicz said he will attend team workouts in early April and OTAs in mid-May before making his decision. He told the newspaper he might also consider just sitting out the 2018 season.
"You can't go repair your brain," he said.
"It's not like an ACL or shoulder. That's serious. I took some dingers. There was a couple of weeks there where I was having some tough times. This is what I've done my whole life, so to think that I'm going to walk away is tough. It's not something that I thought of doing, because I signed the new deal, anytime soon. Life goes on, whatever happens."