Mark Warburton was left frustrated that his side took nothing from the game against Aston Villa despite a strong second-half performance.
Daryl Murphy pulled Forest level after Albert Adomah had given Villa a half-time lead and Warburton was left rueing what could have been as Conor Hourihane's free kick sealed the three points for the home side.
He said: "It is frustrating as we came out in the first 15 minutes of the game and we were very good. We dominated, looked bright and threatening and then we gave away a very poor goal again and find ourselves 1-0 down.
"The 20 minutes after that we were really poor and I think it was the worst we have been in the six months or so I have been here. We looked lethargic, we didn't get out there and we had words at half time as a group.
"The reaction was good and they showed their character and their quality in the second half but it is another soft goal to give away and we come away frustrated."
Warburton knows that his side must cut out the mistakes and stop conceding soft goals as they are giving themselves an uphill task to get points from games.
"There are no excuses and we take blame as a team as we take credit as a team," he added. "We gave the ball away, went long inexplicably and goals change games.
"We had a good response after half time and I thought Daryl took his goal really well with a real calmness and then I thought there was only one team in it. We were attacking and moving the ball well and I can't think of a save Jordan had to make in the second half. But it is irrelevant as we need to take our rewards.
"You can't come to a place like Villa Park and have to score three to win the game. That is what we are leaving ourselves at the moment. We maybe lacked a bit of quality in the final third but we were dominant in the second half and to come away with nothing is really frustrating."