Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear about Toby's strange behaviors of moving his head side to side, incoordination, and unsteadiness after a car ride today.
It is certainly possible that Toby has an ear infection and that is causing pressure and discomfort in his ear that is affecting his vestibular, or balance, system located in his inner ear leading to his symptoms.
Unfortunately because he is a King Charles Cavalier we do need to worry about other more serious conditions that can cause these symptoms.
Primary secretory otitis media (PSOM) is an inflammation of the middle ear caused by thick, glue like mucous filling the middle ear. It seems to affect the Cavalier King Charles Spaniel (CKCs) in particular. The outer ear will look completely normal, but the middle ear is affected.
Initially the dog will only have pressure in his ear head and neck, but as the disease continues we can see balance problems, his lip or ear may droop, drooling, an inability to blink his eye, and nystagmus (involuntary, rhythmic, rapid movement of the eyeball), a head tilt and/or hearing loss.
Diagnosis is achieved via radiographs, an MRI or CT scan. Treatment is removal of the fluid from the middle ear, which in many cases must be done repeatedly.
Chiari-like Malformation and Syringomyelia (CM/SM) is a neurologic condition that commonly occurs in Cavalier King Charles Spaniels. It is caused by an accumulation of spinal fluid within the spinal cord in the neck region. This fluid accumulation is secondary to a malformation of the brain and skull. Basically because the brain is too big for the skull the back of skull cannot accommodate the brain. The back part of the brain (cerebellum) herniates out into the spinal column canal which then interferes with the movement of spinal fluid, resulting in accumulation of spinal fluid within the spinal cord. The pressure of the fluid accumulation leads to clinical signs of the disease. These signs include discomfort or pain in the neck region. This pain can cause symptoms such as scratching on one side, often without making skin contact, so the disease is also referred to as “neck scratcher’s disease.” Facial pain can also be a problem, which can be confused with ear pain. Eventually the pain can become very severe. Neurological signs can also include front limb weakness, rear leg incoordination, loss of sensation, facial nerve paralysis, deafness, seizures, incoordination and loss of balance, vision loss, and head tremors.
This is diagnosed most in younger dogs, but can show symptoms at any age.
The only way to definitively diagnose CM/SM is an MRI of the brain and neck.
Treatment of CM/SM can be provided either medically with drugs to control the pain or surgically. Surgical treatment is usually done in dogs that do not improve with medical management.
Your fellow may have a simple external or middle ear infection, but it may be something more serious so I do recommend that he see his regular veterinarian soon. Because he is eating and drinking normally I don't think that this is an emergency tonight, but I do recommend keeping him off stairs and furniture so he doesn't stumble and hurt himself given his incoordination and unsteady stance now.
Please let me know if you have any further questions.