Thanks for the responses, guys. It is always better to hear from my peers vs. a generic book.
I'd like to learn more about this technique that was mentioned:
"When things get tough that's the time to pull shutters down on real world thoughts. It's a difficult technique, but I can create an almost physical blackness to unwanted stimulus. Took a while to learn that."
Can you give more details about how you reached such a high level of mental discipline?