Colin Cooper admitted Hartlepool were not at the races as they fell to a surprising 2-0 loss at struggling Northampton.
Goals from Mathias Kouo-Doumbe and Brennan Dickenson either side of the break were enough to give the struggling Cobblers a crucial victory.
Cooper said: "We had half an hour in the dressing room and the lads were very honest. They didn't feel, for whatever reason, that it was their day.
"Some felt leggy, some felt tired and we don't know why that is. We made two changes to freshen things up a little bit but it hasn't quite worked.
"We're all leaving disappointed. They were soft goals that we conceded; you can pick the bones out of every goal you concede.
"I don't think it's an individual thing or a collective thing but we were definitely flat. We can't do anything about it, we just need a positive reaction now. I have to say Northampton worked their socks off but too many crosses came into our box and (there was) too many chances for them to score goals."