The Lions have an immediate chance to make amends for the 3-0 defeat when they host Blackburn on Tuesday night.
Millwall's run to the FA Cup semi-final has left them with a backlog of fixtures and, Jackett admits, a few tired legs.
They have three home games in a row against Rovers, Nottingham Forest and Crystal Palace, and still need a couple of points to be sure of avoiding relegation.
Jackett said: "The side lacked energy and sparkle, not necessarily commitment, but certainly sparkle.
"From our point of view we still have four games left and the equation does lie with getting a team that has the energy to get the points we need at home.
"We have to lick our wounds, make sure we get it right and have a freshness and move on again.
"I'm obviously concerned, but we have to look forward and focus on our three home games in a row. We must get over it quickly."