Goals from Guirane N'Daw, Luke Hyam and Daryl Murphy at Portman Road stunned in-form Forest and lifted the hosts out of the bottom three for the first time since McCarthy took charge.
But the Yorkshireman knows his side must now find some consistency if they are to avoid being in the drop zone at the end of the season.
"Unless I've woken up and it's May 4th, I'm not bothered," he said. "We'll all get a kick from seeing it but we've got tough games coming up.
"We've got to maintain that level of performance and make sure we stay out of it. There's no time for patting each other on the back or stroking each other's egos.
"I enjoyed it and we played well, but now we've got to play like that every week. If you look through the team, everyone played well. Now we've got to do it again and again."