Going through every aspect of an event in your head before an event is a

Mental Rehearsal

Explanation:

It prepares the mind for what’s coming in the event and perform becomes much more natural and unconscious. The unconscious mind runs the body and therefore physical activities are done unconsciously. By doing mental rehearsal, you are communication with the unconscious mind in the way it likes it best (through pictures, sounds, feelings, tastes and smell). By rehearsing, you are making the situation more familiar, which as a result makes you more comfortable.