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.
Cash said: "We are really disappointed. We always knew it was a tough place to come. The first 60 minutes we did well but maybe we lost a bit of control in the last 30 minutes. We are really disappointed at the end.
"It is tough. You have to come to places like this and be strong and try and get three points. We didn't do enough to get that but we pick ourselves up and go again next week.
"Everyone is important. We have built a good team bond here and we have a string squad with a fantastic manager. The challenge is to finish as high up as we can. We will go again and look to bounce back."