I would suggest taking small breaks in between your sessions to give your eardrums a break. Ear fatigue can lead to over compensating when eq'ing, mixing, etc. And dont mix when you're drunk, stoned, or whatever. What sounds good to you at the time will not sound so hot the next day. I speak from experience
Now writing when you're drunk, stoned, or whatever...that's a different story. Also, a good set of earplugs at the club doesn't hurt. You can still hear what's going on and you'll also be able to hear the next day as well.