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This sounds like Geriatric Dog Vestibular Disease. It is a common condition in older dogs (hence the name). We do not know what causes it, but it appears to be a condition affecting the nerves of the inner ear that control balance.
While this looks terribly awful, it usually does not require treatment and should resolve on its own. There is no specific treatment for the condition. However, if Flossie should not be able to drink and hold down water, or vomits repeatedly, then she will need supportive care (fluids and medications to control the vomiting). The drooling you are seeing is nausea due to her feeling of dizziness.
It may take several days for her to walk straight again and she may have a slight residual head tilt.
Dogs that have this condition often get a repeat bout in the other ear at some point in the future.
Contrary to what many veterinarians call it, this is not a stroke and has no predictions about her future health.
Hope this helps ease your mind
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No doctor patient relationship is formed by this communication. This advice is no substitute for a complete physical examination and appropriate diagnostics provided by a licensed veterinarian.