Heyward, who was activated from the 7-day concussion disabled list Friday, said he discovered how "scary" head injuries could be.
"It made a believer out of me," Heyward said Friday afternoon. "Not that I wasn't a believer before. You feel for anyone that goes through it. That stuff is scary. You don't feel like yourself, and you don't see anything wrong with you physically, but there is something that's not right."
Heyward, 28, banged his head against the right-field wall as he attempted to rob Dexter Fowler of a walk-off home run at Busch Stadium in St. Louis on May 6. He busted his lip on the play, but it wasn't until a day or two later that he started to feel the effects of hitting the wall. He said he assumed at the time it was normal soreness after a long night.
"I noticed my head wasn't feeling right," Heyward said. "I wasn't going to say anything, and then eventually, I was glad I did."
Though Heyward was eligible to come off the disabled list Monday, he said he wasn't ready.
"Day three, I woke up and I was like, 'OK, I feel good,' then I got to the field, and it was not anywhere near normal. It was frustrating. There were days where I was sad, down, but it was good to be around the guys."
Heyward said it was only over the past couple of days that he got his energy back and started to feel like himself. The Cubs went "above and beyond" to make sure he was OK, according to Heyward.
"Just making sure nothing is going to come back from it," he said.
Manager Joe Maddon added: "He started to smile again. I heard the laughter, and I knew it was getting better."
Heyward said he won't change his style of play, and the Cubs won't ask him to, according to Maddon.
"I wouldn't say that to him," Maddon said. "I think that's who he is. That's a big part of his game. A big part of his contribution is what he does with his glove."