chronic headache and ear fullness
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When you blow into your ears by holding your nose, you increase the pressure in your inner ear. If the pressure in your cerebrospinal fluid (CSF) is so high it is pressing your brain, which is soft tissue, into the openings of your skull, the momentary increase in the pressure in your inner ear could partially balance the too high pressure in your CSF, giving you a brief feeling of relief.
Ask your doctors to measure the pressure in your CSF.
Holding your nose and blowing into your ears would increase pressure in your middle ear, not your inner ear. Also, the anatomy of the inner ear appears to be such that the pressure in your inner ear will be the same as in your CSF.
The periodic episodes of vertigo and feelings of fullness in your ears you describe are both symptoms of Meniere's disease.
I do still think it might be a good idea to assess your CSF pressure.