One of the most important lessons for 24 Hour Comics Day is ... well, I want to say "Don't Give Up" straight off but I can't.
It's "Know Your Limits".
Need a bathroom break? Go. Hungry? Eat something. Wrists hurting? For the love of all your tendons, take a break (and some ibuprofen, or do stretches, or a hot/cold contrast bath ... seriously. RSI is no fun and it can knock you out of commission for six to nine months at a time ... and I'm speaking from experience).
But if while respecting your limits ... you have to recognize when your brain's just fucking with ya, and push through it.