Tottenham were 3-0 winners at Craven Cottage in Saturday's London derby, and Fulham have slipped to 13th in the Premier League table after only picking up one point in their last four games.
Sidwell admitted that his side need to turn things around but he believes that Saturday's result flattered Spurs.
"The first half was very even, our game-plan worked. But they were three disappointing goals in the second half.
"The result was a bit harsh considering the effort and the performance," he told the London Evening Standard.
"Now we're on a bit of a bad run so we have to start picking up.
"We have to dust ourselves down and go again next week."