What do you worry about when improvising on the organ?
A lot of us worry about not knowing what to play. We don't trust ourselves.
So we try to memorize our improvisations. Sometimes we write them out like compositions and then commit them to memory, sometimes we repeat passages over and over until they're become second nature.
I'm not sure if that's the ideal way to go about improvisation. Puts a lot of stress on the perfect and flawless performance. This creates fear. With fear and anxiety, we can't function properly in front of other people.
A more relaxed way is when we simply tell a musical story. A real one.
Without ever memorizing a thing. But noticing opportunities that present themselves. Always conscious of the story arch.
Mark Twain was right. Tell the truth.