As someone who is predisposed to an unhealthy amount of self-analysis, here are some of the things I consider to drive away the fear/anxiety and keep the studio practice spritely:
Joy gives you power.
My variety of painting is like any necessary human expression such as singing or dance.
It's about play, so how are you getting so down about it?
I know I've made something worth saving before. It will happen again. Have faith.
You are totally freaking free!! This is your chance to make real all or any of those things bouncing through your skull.
Don't be impatient. Let the painting reveal itself to you through the ACT of painting, not just in THINKING about it.
Judgements you make don't need to carry so much positive or negative weight. This is from a part of you concerned with illusory ideas of success/failure. As long as you're thinking of those ideas, you certainly won't make a good painting!