Definition: a feeling of anxiety and self-doubt that can arise at any distance up to half-way between a person’s destination and their last recently locked door.
Lock-doubt leads to such immediately nerve-inducing questions as: Is the car/house still open? Will someone try the handle? Am I close enough to go back and check? How annoyed will I be if I go back and it is locked, just like last time? What if I go back and it’s already gone?
It can be said that being locked-out beats having lock-doubt.