The England international struck the winner at former club Chelsea on Sunday.
Describing Sunday's game as "probably the best I have felt", Johnson said: "Hopefully the injuries are behind me now."
"It was great to score," said Johnson, who spent four years at Chelsea.
"There was plenty of space all day and I told Charlie I was waiting 75 minutes for that pass.
"He'd been trying to do that all game but once was enough. It was a good goal and I'm pleased.
"I tried not to celebrate too much because I had a few great years here, but when you score a late winner like that, it's hard not to celebrate.
"We finished the stronger. We dominated the first half but Chelsea are a great side and we expected a reaction.
"Chelsea will have periods whoever they play when they are on top and I thought we dealt with it quite well other than the goal.
"We showed great character to bounce back. Last time out (against Swansea) was disappointing so to come here and win was fantastic.
"We are aiming for the top four - that's what we are fighting for."