Jaspar has become sometimes fearful now of certain places -- roads we do not know well, near the light rail tracks for example (he is fearless off or on lead in a park though or anywhere he knows well). This out of the blue as well -- my guess is that it is associated with his increasing deafness in some way.
So I also echo that it is worth checking physical possibilities first with a vet.
I know my CPDT certified trainer friends would say to get a very thorough vet check and consider too the possibilty of pain (could a harness be rubbing? Disk pain? SM pain? Anything that would make a walk now an unpleasant experience?). Maybe mild dementia starting so confusion is causing fear?
These can be really hard source problems to identify. I hope it is something you can pinpoint that isn't very stressful or serious and address easily.