Brief Answer:
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Detailed Answer:
I read your question carefully and I appreciate your concern about your uncle.

Since you say he's had a physical recently I am assuming signs indicating heart issues or general conditions like anemia, liver or kidney disease have been excluded.

So looking at other possible causes, a common cause is inner ear conditions, an organ which is very much involved in balance. Usually the dizziness takes the form of vertigo (sensation of spinning), often influenced by changes in head position. Antihistaminics like meclizine can help.

Another possible cause could be neck problems like arthritis, which can lead to compression of upper cervical nerve roots. These nerves are also involved in balance as they provide the brain with information on head and neck position. An xray, can help in diagnose, at times neck MRI is recommended. Physical therapy is the mainstay of treatment.

Looking at history of bypass, meaning he is an individual with a high risk of vessel disease in other areas, one more alternative might be stenosis (narrowing) of the neck vessels, like the vertebral arteries. These vessels supply with blood the posterior part of the brain responsible for balance, so their narrowing might lead to transitory low perfusion and signs. Can be evaluated by ultrasound or by CT/MRI of blood vessels.

I remain at your disposal for further questions.

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