The Albion boss said: "It was a disastrous 45 minutes for us. As good as we were in the first half as poor as we were in the second half.
"We said at half-time not to give them any encouragement, to keep playing the same way as we had in the first half. That message wasn't taken on board but you have to give Brentford credit for the way they came out in the second half.
"If you can get through to the hour mark then it demoralises the opposition but their goal went in within five minutes, that got their tails up and gave them plenty of encouragement.
"It's the same players and the same formation that has defended so well over the last six and a half games but it is difficult to analyse too much and we have to give them credit."
Albion went behind in controversial fashion in the first period conceding while Kyle McFadzean was down injured.
Clough said: "We had a man down with a head injury and the guideline is that the ref should stop the game but we don't seem to get certain decisions and then we miss as good a chance as there has been in the game to go 4-3 up so that is how close we were.
"Comebacks happen but when it's 3-3 you try not to lose the game - that's the principle we are trying to get through to the players.
"It's a long two weeks now to think about it but we are still out of the bottom three just - and I think it will be like this for the next eight games."