In a recent interview on 610, J.J. Watt opened up on the pain he went through during the 2015 season.
The 2015 season ended not only with a Hoyerible quarterback performance, but with J.J. Watt laying on the ground in pain as if he was a mortal man who could feel things, not the football universe destroying deity we know him to be. The reason for it was a groin injury. And shortly after the season ended, he was cut open so it could be repaired.
That was just one of a few injuries he played through in 2015.