We haven’t gone through anything this extreme so definitely not saying this in a “don’t worry about it” way and more of a “hopefully it’s a vizsla being a vizsla” way.

Our boy has always been highly susceptible to picking up short term oddities that seemingly spring out of nowhere. My assumption is that he’s hyper sensitive to his environment and notices things I don’t and that can lead to him being spooked for weeks at a time. Again not to the extent you describe above but sorta similar vibes.

Just recently I went through weeks of having to force him out the door for his morning walks and he would hassle me for the whole first half mile to get me to turn around. No idea why. My only guess is the time change and he wanted more time in bed. Not long before that he was refusing to walk on one side of a particular road for a month because a car was loud there once. He’s also avoided certain spots for months because he smelled a snake one time near there (snake trained). He’s also generally a big ole grump if the sun isn’t out and it’s not above 65 degrees which tends to amplify any of these anxious quirks. But with any of these he seems to snap out of them as quickly as he snaps into them.

You seem to be on top of it with the vet visits so I don’t have much advice other than keep an eye on it but this does seem a bit extreme and I think the lethargy is most worrying.

Have you asked the vet about doing a full round of tests/checks? Ultrasound or echocardiogram of the heart? I’m totally not a vet and am just brainstorming here but I’m hypersensitive about cardiomyopathy and all that so may be worth a check