And while he’s since returned to acting -- and even done more stunt work -- O’Brien says the period of his recovery has felt much longer than the calendar shows.
“In a lot of ways, those six months went by like that,” he explains. “I can still remember that six months as if it was five years of my life.”
In July, O’Brien talked to ET's Leanne Aguilera about filming after his recovery at the American Assassin press junket.
"The state that you're in after something like that, you just want to run from all that stuff," he shared. "I didn't really even want to leave my couch necessarily when I was allowed to, so yeah, it was a big step doing this."
"I ultimately decided that I wanted to try it and I didn't want to let it go," he added. "[The movie] ended up being really instrumental in the whole process."