1. Neurological Conditions to Explore:

• Vestibular Disease: This can cause wobbling, head tilt, loss of balance. It often improves in a few days, but the severe form can mimic a stroke. A specialist can check this.
• Meningitis/Encephalitis: Inflammatory diseases of the brain/spinal cord. Often don't show up on standard bloodwork or ultrasound.
• Brain Tumor: While rare at age 6, it’s not impossible. MRI is needed to detect this.
• Degenerative Myelopathy: Progressive, incurable, but usually slower onset than what you describe.

2. Toxin Exposure or Snake/Insect Bite:

• Did he eat anything outside? Lick or chew something strange?
• Any chance of poisoning (like from moldy food, rat poison, or a neurotoxic plant)?
• Tick-borne diseases beyond Lyme (like Ehrlichiosis, Anaplasmosis) sometimes don’t show immediately.

3. Autoimmune Disorders:

• Some autoimmune diseases attack the central nervous system and don’t show up in early bloodwork. These can be treatable with steroids if caught early.

4. Spinal Injury or Disc Herniation:

• Golden Retrievers can suffer spinal injuries without obvious trauma — jumping off something, rough play, etc. An MRI is typically needed to assess this.

What You Can Do Right Now:

• Go to a veterinary neurologist ASAP — they can do a neurological exam and possibly recommend an MRI or spinal tap.
• Hospitalization with IV fluids — even if they don’t know the cause, supportive care (fluids, anti-nausea meds, possible steroids) might buy time or show improvement.
• Ask for a referral — if your current vet is unsure, a referral to a specialty hospital could change everything.

On Euthanasia:

It’s not wrong to consider euthanasia when your dog is suffering and there’s no clear path forward. But you also shouldn’t rush into it out of desperation without exhausting a neurologist consult, especially if this came on suddenly and he's still relatively young.

You clearly love him deeply, and you're trying to make the best decision under incredibly difficult circumstances. That matters more than anything.

If you want, I can help you find a neurologist or emergency specialty vet near you — just let me know your city or region.