Paul Sturrock accused his Southend side of disrespecting Barnet after their 2-0 defeat at Underhill in League Two on Tuesday.
Sturrock's men remain outside the top seven after goals from Jake Hyde and one claimed by both Dani Lopez and Bees player-boss Edgar Davids boosted the hosts' survival hopes and kept them above the League Two drop zone.
After seeing his men reach the Johnstone's Paint Trophy final at Wembley before winning at Wycombe at the weekend, Sturrock admits he was disappointed with their display against a side battling to avoid the drop.
"After the last three performances, getting to a cup final and a good result and performance on Saturday, it just shows you what a poor mental approach can do to your team," said the Scot.
"I think we decided disrespectfully we just needed to turn up. I thought the first 15 minutes we did okay but after that our attitude was bad and we didn't perform to the standards we can achieve.
"I don't know if it is a mental thing but it wasn't just one or two. We played with about seven or eight who weren't at the races compared to the standards we have been achieving.
"I'm bitterly disappointed with their approach. At the end of the day we definitely deserved to lose.
"If we are to get automatic promotion we probably have to win all of our games now, and if we are to get the play-offs we can't afford many more slip-ups."