Most often we slip on the turning point. It's simple physics - our body is still moving forward but underneath our feet there is too little traction to make a turn. And so we slip.
Improvising organ music is like running on ice. We don't play the wrong notes when the musical road is straightforward. Usually we only slip when there is a turn - a change in texture, rhythm, melodic direction, harmony, or registration.
What do we do after we slip? We get up and continue running. Exactly.