I think i'm a great player when my mind is right, but often times after winning a big session i'll come back and play totally loose and lose that money I won. I think with my mentality I cannot be a winning player this way unless I can change this. I am young and I guess do not have the patience to do the same grind over and over.....
What you're describing is "winner's tilt."
You need to mentally remind yourself during play and also when playing after a big winning session to "stick to my game, just stick to my game." Basically remind yourself to not get looser as you win and stick to your strategies that got you to the wins (as long as of course it was a winning strategy and not just all luck and suckouts!)
You can also consider setting timers to take breaks or leave sessions or also consider leaving a table if you're up a lot. While pure strategy wise it's not often best to leave when up a lot, it can help with control and discipline to protect your winnings while you work on your mental game aspects.
There's also books like Zen and the Art of Poker as well as The Mental Game of Poker.
As long as you aren't losing money you can't afford to lose, what you describe is a part of mental game in poker and can be worked on.
