Hmm... I know where you're coming from, I think. I've worked 15 hour days, that used to be my work day. Now I still do work 15 hour days from time to time, but not every day. If that's what you're going through, all I can say is smash that coffee and get as much rest as you can. I aim for 6 hours of sleep minimum. When I set my alarm for the morning and see 7+ hours until it goes off, I feel like tomorrow is going to be a good day.