Welcome to HealthcareMagic forum
The cause of the dizziness
could be due to blood clots
in the brain (infarct) which will cause damage to the particular area of the brain leading to various neurological problems. Posterior ethmoid sinusitis
is not a thing to be concerned as brain is more important than the sinus.
Your doctor is right, neurologist
is an ideal doctor to treat this condition and your father will require blood thinners and anti-edema medicines to reduce the further damage to the brain.
Hope this answers your query; I wish him good health.