It's like running up the stairs and stepping wrong because you tried to keep going upward past the top step.
This almost always happens to me after I finish drafting a novel. For some reason, the sensation has been very strong this week. I know from experience that it's a bad idea to view this phenomenon as a form of momentum and try to keep writing. The writer brain must be allowed to reset and recalibrate.
Still, why aren't we writing?