Forest lost 2-1, with all three goals coming inside the opening 15 minutes.
“First half was very difficult,” Pereira said. “To press in the way we want to, we need energy. In the first half, we tried to press as if we had a full tank of energy.
“What we learned from the first half is about the trigger to press together. We started to press individually, thinking we had a full tank of energy to press.
“We conceded space we cannot concede against this type of team. We reacted to the goal and equalised, but we still had the same problems defending.
“They (Brighton) prepared in seven days, not in three days as we did. They tried to press us and we didn’t find the proper spaces to go. They scored again after a mistake.
“We adjusted the system in the second half. We didn’t concede anything to them and we had one or two chances.
“We lost an opportunity to get points. We should put our focus on this game because the next game is (Manchester) City; it means recover and try to rest and prepare to face them, not think about the future because we don ‘t know what will happen in the future.
“We tried to get points from this game, but it was not possible. We need to learn from the first half and take the good things from the second half.”