He told the club's official website: "I couldn't breathe when I saw the ball go in.
"I hit it and knew as soon as I did that it was going in but it all just happened so fast I didn't know what to do.
"I did plan a celebration for my first goal but I just completely forgot about it because I was so happy to score."
The goal also came as a relief to Gunnarsson following a bet with team-mate Robbie Simpson not to shave until one of them had scored. He added: "It was just a bet of a bet between me and Simmo and now I've scored I'm glad I can get it all off."