Forest came from 1-0 down to win on Saturday night 2-1 with goals from Nikola Milenkovic and Anthony Elanga in the final ten minutes after Jhon Duran had put the visitors ahead.
Emery said, "We played 90 minutes more or less as we planned. In the first 70 minutes, we were controlling and kept the ball possession. Nottingham Forest are very aggressive in attack. We lost the control completely in the final 20 minutes because they started pushing more and made some changes.
"We had to be consistent with the ball. We had to keep the possession and should have tried to attack and score the second goal.
"But of course it is a process. We are in a process. We will analyse the first 70 minutes and also the last 20 minutes and where we have improve the team is very clear to me."
On the Morgan Rogers penalty incident, he said: "I can't tell something about the referee and the penalty. It's again how we played and how we continue doing the process. It's a tough match and they are now ahead of us. They have 28 points. It was a very good test against a team comfortable and strong. They deserved in the last 20 minutes to come back and get the result."
On Duran's performance, Emery added: "I prefer to change. It's good for him and the team. We need to be defensively strong and we have to add individual skills and performances to get goals like he did."