I have had it in the past and it is a challenge to overcome. I tried everything including hypnosis (which helped by the way). I think the best solution is to change your drawing and holding routine. If you normally draw and bring your pin up on your target, try bringing the pin down from the top. Or put the pin on your target before you draw and keep it there during the draw. Practice drawing and holding without releasing. Let down and draw again, this time release.
It's going to take work, but you'll eventually beat it.