A Mikele Leigertwood goal 10 minutes from time earned Reading a return ticket to the big time four years after they were relegated. Combined with West Ham's draw at Bristol City, their win ensures them a top-two finish. They sit three points clear of Southampton with two games left to play in the title race.
A delighted McDermott said: "This is my best moment in football. My worst was on the pitch at Wembley on May 30 (last year's play-off final defeat to Swansea). We are in the Premier League now and I can celebrate for the next two months. I need to get away for a while in the summer and have a break."
The final whistle sparked a mass pitch invasion by excited home fans and then an appearance in the directors' box by the Reading players.
There was also some joy for Forest who, despite their defeat, are guaranteed survival in the npower Championship thanks to results elsewhere.
McDermott added: "Tonight was the most important three points we have got this season because it has seen us over the line. I don't know how I am supposed to be. I had the worst summer last season after losing the play off final against Swansea but this will be a good summer.
"I didn't actually know the West Ham result until after our game had finished but I sensed it from the way the crowd was reacting. It's really strange. It doesn't seem real at the moment and it doesn't feel as if it is happening to me.
"Now I will simply concentrate on our next game at home to Crystal Place because that's in my nature. I thought we were a bit nervous tonight and we weren't as fluid as we can be."
McDermott praised Jason Roberts, saying: "Jason has been crucial to us but we were doing well before he arrived. I have been lucky with my players and staff. They have carried me on.
"We have had difficult times and had to sell our best players but now it will be a good summer. The players will have tomorrow off but then it's back into training for the next game."