The North East club threw away the lead to lose 3-1 at bottom club Queens Park Rangers on Saturday afternoon and are now just six points clear of the drop zone.
Sunderland next have back-to-back home games against Norwich City and then table-topping Manchester United and O'Neill is aware his squad need to battle.
"It's a tough old set of fixtures for us between now and the end of the season," he said. "We need to get some points on the board.
"The players in the dressing room are disappointed but we're looking to respond as we have done before. It's a big game next week."
Sunderland had gone in front at Loftus Road through Steven Fletcher but QPR, having defeated Southampton last weekend, hit back thanks to Loic Remy, a stunning Andros Townsend strike and Jermaine Jenas.
And O'Neill said: "It was always going to be a difficult game for us.
"QPR were buoyed by their win over Southampton last week and we had to counteract that and deal with the swell of euphoria from the crowd, which I thought we did well.
"We put ourselves in front and it's a wonder goal from them to take the game to 2-1."