The 31-year-old Irishman “can’t help” continuing to train even during his time off and admitted he would miss the camaraderie of the game if he was no longer involved.
He told Rugby World magazine: “Whenever we have a few days off with Ulster, I can’t help myself, I have to go in training.
“I guess that’s because I love it.
“If it wasn’t there, I’d miss the atmosphere, the vibe you get from playing with mates, having the craic with the lads.
“A part of me is slightly worried about how I’ll cope outside rugby once it’s all over. If I don’t have that, which I won’t whenever I retire, what do I do?”
The Ulster lock feels “incredibly fortunate” to make a living from something he loves.
He said: “Being part of these Ulster and Ireland teams is a massive enjoyment for me.
“When I was younger I wanted a job that I could really enjoy. That’s what I always hoped for.
"If you love your work, you’re in a pretty good place in life and I’ve been incredibly fortunate because that’s what I’ve had for over a dozen years now. It’s the main thing that keeps me going.”
Despite his passion for the game, Iain has always found it easy to switch off and unwind after a game, which he credits his young family for.
He said: “It’s something I’ve always been good at and having two young kids at home has made it all the easier.
“Well, I say young but they’re almost four and almost six, so they’re growing up fast. They’re amazing.
“They haven’t a clue about rugby and irrespective of playing the worst game of your life and feeling as low as you’ve felt, once you walk through the door they’re the greatest cure. Suzanne and the kids keep me grounded.”