1st lesson - When in a slump, do not dig yourself deeper by playing like an idiot. I did this when i was down about 5 buyins, feeling like i had to make up what i lost. I ended up having to dig myself out of a bigger hole because i began to chase draws and overplay hands. I could be much more ahead if i didn't act stupid originally.
2nd lesson - Taking a break really helps. It was only for a few days, but it gave me that feeling of starting over. I was able to clear my head and become refreshed, and it improved my judgement considerably. Many have given this advice before, but i wanted to give an example of where it really helped
3rd lesson - You need to have patience! Remember that no matter how far down you are, you can't make it all up in one day. In fact it took me 2 months because i played at a slower pace so i could really play my A game. I waited for the cards to come, and they did! I wouldn't say it was a great run of cards, but it was better than the first 3K hands.
4th lesson - Trust your game. I used my abilities without questioning them during the comeback. I was successfull at the limit below, so i believed i could do the same here.
All in all, you notice that all of the advice above really didn't have to do a lot with the actual card playing. It was a lot of the mental stuff that got me through it. Remember, poker is just as much about yourself as it is about the cards. Good Luck at the tables everyone.