With 20+ years of competitive martial arts experience I know that I and others have experienced utter exhaustion in the initial minutes or seconds in the first match. There are a lot of moving parts going into this experience. The excitement of a match is enough to drain someone physically and emotionally. Like most treatments to anxiety there has to be a degree of exposure therapy. Long and paced bouts of exercise and sparring don't necessarily translate to competition. Being more deliberate and focused on specific aspects of training is tricky. There are a lot of moving parts in things like Judo and Brazilian Jiu Jitsu. Many people get caught up with the "more is better" approach, with the idea is if they just put the time the results will speak for themselves. By trying to do everything nothing is ever accomplished.