Interesting John Lahr article in the current New Yorker on Stagefright. Unfortunately, not available online. A lot about fear and what some performers, who can, do to overcome it. Definitely worth a look.
...the American psycho-analyst Christopher Bollas, who has treated many stage and screen actors, says. "You lose your radar - like a surfer. You can ride a ten-foot wave with real confidence, not thinking about it, just doing it. Then, all of a sudden, you become too self-aware. You think too much. You get wiped out." The paradox of acting is that, like surfing, it requires both relaxation and concentration. If there is concentration without relaxation, or relaxation without concentration, the performance doesn't work.