Many choices
There are many books and videos available showing and explaining how to prepare ones mind for stressful times and events and an important pool game, match or tournament certainly meets this criteria.
It does not have to be specifically about pool as all sports have this stress. When I was training with my departments trainers for firearms instructor school and tactics we spent a lot of time on mental preparation and the effect of stress on our body and all of it gave tools that I apply to pool and other potentially stressful situations.
My favorite for pool is to watch the guys from the Philippines. They know how to loose and bounce back, how to win and keep winning. They know they will win and loose, they know they will make and miss shots, they just push through it and learn from it and come out better for it.
Many guys and I was one of them once, think stress does not effect them, once we admit we are all effected by stress we can learn to manage it better as it effects us all and usually does not manifest it self in a "total break down", but it does effect our performance, especially when we are not aware of it.