"There is a different atmosphere to training when you've lost a few games," O'Neill told Villa's website. "It's not that people don't enjoy training because when they get out on the pitch they are fine.
"I'm not saying that it's disappeared but it goes into the back pocket for a moment.
"We'll get it right. It's far from doom and gloom around the place though because I think overall we're doing well."
Despite two straight home defeats, O'Neill picked out the Portsmouth game as the major source of the players' frustration.
"There's natural dissatisfaction because of two straight defeats. Portsmouth in particular was disappointing because we went into the game thinking we could win it.
"The goals came at really bad times for us. We were on the back foot immediately after an early own-goal and then Muntari scored an absolute screamer when we were forcing the pace and trying to get back into the game.
"We went in at half-time 2-0 down but we could have been 2-2 at least. Gabby had a chance just before half-time and earlier it looked easier for Martin Laursen to score than to miss with a header.
"Even at 2-0 going into the second half, I still felt we were in the game but then Muntari scored again."