downs
The best thing I can say is that it definitely gets better. At some point you will realize that the struggle is really with yourself, not the casino. All the rah rah self-confidence in the world is not going to change the outcome of one single hand. That is the best part about it.
After you have been doing it for awhile, you will begin to realize that all the ups and downs, the hot streaks and cold streaks, are all in your head. External reality just keeps moving along.
What does that mean? It means play a perfect game every single time, and leave the emotional ups and downs for the beginners. There is no place for beating up on yourself any more than there is a place for thinking you are King of the World for having made some brilliant play. No matter how far up you are, or how far down you are, it doesn't matter--the present state of your psyche and your bankroll have no influence whatsoever on the outcome of the next hand.
Once you understand that, you will understand that your obligation to yourself is to play your very best at all times. It took me several years to reach that point (and more money than I would care to admit), but once you understand that your moods only affect you, not the outcome of the hands, it all gets a lot easier.
If you are unclear about the issue, there is a very readable (for having such a ponderous title) paper called, "Cognitive Heuristics and Biases in Behavioral Auditing," by Tversky and Kahneman. It is a fairly easy read, and will give you a lot of insight into the mental traps you can set for (and spring on) yourself.
I would also suggest that anyone interested in longevity as a counter read and study everything they can lay their hands on about decision-theory and decision biases.
Good Luck!