O'Neill admitted he feared the worst when he first took over the club after defeat at Wolves in December.
He said: "I was prepared for a relegation scrap. My first target was to think about getting a point per game and if that had been achieved after 30 games I'd have been delighted.
"The lack of confidence was my biggest worry. I wouldn't pretend I knew everything about the players' ability or about the strength in depth here but confidence was the main thing and after losing a game like that, it was severely dented.
"When you're in a real relegation struggle you look at your real experience players to help you out. We did the opposite with James McClean who gave us an enormous lift and has carried that through and then you have a player with the ability of Sess which gives you a bit of heart."