There's a large mental component to squash. While I try not to think about previous points and as hard as I try to remember that each point is independent, I find that rough points creep into my head as I wait to receive the serve. And unfortunately, the frustration of giving up unforced errors often begets more unforced errors.
When I'm behind, I try to break the game to 11 into subgames that are best of 5 points. In other words, when I'm trailing by 7, I concentrate on winning the next subgame to 5 by winning the next 3 points. Somehow winning these smaller games feels more achievable.
Whenever you're working on something that feels daunting, try breaking it down in to bite size pieces. It makes it easier to stay focused on what you need to do next.