I don’t try-I win. Then everytime it matters and I really want to win and put in the effort I lose.
My best advice is to enjoy the game. I've been through this several times. You might look into the book "Playing to win" and "The Pleasure of Small Motions."
Without knowing more it's hard to say, but when I get into this state it's because I care too much ("I'm gonna play my best"), which adds stress, which shuts your brain down, which also causes tension in your body. Try breathing in fully and expanding your diaphragm then breathing out fully before you get down on a shot. That full breath in and out releases tension in your body/muscles. It's kind of like target practice, you don't want to be tense when you squeeze/ease the trigger.
Tension sucks, it can get to the point it makes your body hurt, especially if you have any arthritis or old injuries. Cold and wet make it worse. But tension puts your whole body on edge, like a live electric wire. Again, I don't know if this applies to you but it sure gets me from time to time. I notice it the most when I'm trying to "do my best" in a tournament or such. If I just can get out of my head long enough I play way better. Enjoy the feel of the game. Look at the layout and shot selection while up. Take a bit of time. If you're stressed and have tension you tend to rush this step and your game falls off as a result.
You can't win em all, and when you're concerned about winning them all you often lose many that you could have won. I think it was CJ Wiley that said he imagines losing before a game, kind of an exercise to clear your mind and not stress over situations. Basically it lets you clear your mind of the what if's and the stress that comes along with it.
Please let me know if you try anything that works because this is something that haunts me every so often. It's annoying and I agree it's likely mental but damn if this head of mine can get it through my thick skull!