Gerrard underwent groin surgery for an injury sustained in March, and was then hospitalised again after developing a serious infection.
"When I got the injury, I knew it was going to be a serious one, something I wasn't used to - and I'll admit I was down, as low as I've ever been as a footballer," Gerrard told The Mirror.
"I was fighting to get fit, just to get out on the pitch. I was trying to put my body on the line, but it wasn't the real me and I wasn't the player I want to be.
"It probably wasn't until I got off the crutches that I started being really positive again. I could see I was progressing day by day, and when that happens your positivity creeps back in. Without a doubt, the last six months have been the hardest of my career."
The England international made his first start of the season against Manchester United on Saturday, where he scored his team's only goal in a 1-1 draw.