[indigochill]

> Yet in real life I'm useless in front of a piano, or a paint brush. It would be great if there was a way to tap into that creativity once awake.

Imagination and technical skill (that is, how well you use a piano or paint brush) are orthogonal domains. The way to tap into your imagination is to develop your technical skill to the level where you're capable of translating what you imagine to the physical motions necessary to convey it on canvas.