"We never even hit the target with all the chances we created in the second half and these were golden chances, not just half chances.
"That is a particular worry now.
"We have lost four games 1-0 and it is a defining line between whether you draw 0-0, keeping your points up, or if you nick the odd one to get the victories and that is what we were doing in the first 10 games.
"Only four points from the last 21 means we are in a very deep and very bad run at the moment."
Allardyce also attributed his side's lacklustre first half display to a busy run of recent fixtures that Reading have managed to dodge.
"First half I'd say that the legacy of Arsenal, Chelsea - Saturday, Wednesday - and Reading not having a game told on the players," Allardyce added.
"It certainly was apparent that the energy Reading had made life difficult for us because of the fact that we had had to give so much against Arsenal and Chelsea, and Reading played here on the back of a very confident run."