Vocal cord paralysis due to sleeping position?

Hi - My 92 year old father woke up with one of his vocal cords paralyzed in December.  A CT scan of the throat area was normal.  2 months later his voice did come back significantly.  But 3 weeks later, he woke up again after sleeping, with the same problem.   I wonder whether his sleeping position might be putting pressure on the nerve.   He sometimes falls asleep in a reclining chair, with his head titled forward.  But I can't find much information regarding this as the cause of vocal paralysis.  Do you know of anything in the medical literature regarding this possibility?   And if sleeping on the bed is better for this condition, would matter which side he slept in/  I.e. if it was the left vocal cord that was paralyzed, might sleeping on either the right or left side be better?

Is an ENT doctor the correct person to consult with regarding this possibility, or she we be consulting with an orthopedist, a rheumatologist, or a neurologist?  Would any other test (i.e. MRI) help to show whether the nerve is being pressed on in places other than the throat?  Thanks. - Mark