Peter Hartley's late header cancelled out Martin Rowland's seventh-minute penalty opener. Then, four minutes into five minutes of injury time, substitute Luke James drilled in a low volley to make it 2-1 to the hosts and complete the most unlikely of turnarounds at Victoria Park.
"It's a disappointing changing room for sure, it was in our hands - we didn't deserve to lose," Slade said.
"We created chance after chance and paid the price for not taking them. We were one up and, if they were going to score it was a set-piece - they are hugely physical and we didn't deal with it.
"How did it happen? How do I know. We've not picked up, not marked.
"There's no easy way out of it. Hartlepool didn't deserved to win the football match."