Forest won 2-1 in London thanks to Gibbs-White's 89th minute penalty.
"Incredible. It wasn't a nice game," he told Sky Sports. "We knew it was going to be a battle because of the position of both teams. What I liked from the boys is we didn't give up and we fought till the end.
"Again, we seem to keep conceding straight after half-time. When that got disallowed, it changed the momentum of the game. It brought belief in the squad. Delighted we got the three points.
"We should be starting every game with full belief, but it has not been that case recently. Their goal put us on a downer, but we reacted well."
The penalty was awarded for a foul on Gibbs-White by Hammers goalkeeper Alphonse Areola. Gibbs-White said: "To be honest, I got whacked in the face and I didn't have a clue what was going on. I came to my senses when he said it was a penalty.
"No doubts, I was practicing it yesterday. It was a safety one, but we got the three points in the end.
"It is what we want to do, we want to go into the game believing. We have not got to kick on this year, a fresh start. First half we were that one yard off and second half it picked up, and we were good again."