The Bluebirds slipped into the bottom four for the first time this season after a Macauley Bonne-inspired Orient twisted the knife.
Barrow’s defeat - paired with Solihull Moors’ late win at Hartlepool - left the club in a sticky situation.
They now need to do what they haven’t for around five-and-a-half months and that’s win at home.
Pennock said: “We let in some very sloppy ones and when you do that you gives yourselves a mountain to climb.
“Leyton Orient deserved the win, they were on top of us and now we have got to move on and very quickly.
“I’ve told the players they can afford to feel down. They have put themselves in this position and now is the time to roll up their sleeves. We have got to get on with it now. We can’t sulk. If we sulk we go down.
“We now have a crucial couple of matches ahead of us and it’s about getting our heads down and focusing on what we need to do.
“We need to win at home, it’s as simple as that now. It’s a big week.”