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Middle ears are connected with nasopharynx
through Eustachian tube.
Partially or completely blocked eustachian tubes can give a sensation of pressure/fullness in the ears.
While you come down from mountains, out side air pressure increases. Eustachian tube opens frequently and allow air entry in the middle ear, to equalize pressure. And if your eustachian tubes are not functioning normally, relatively more out side air pressure will push your ear drum inwards. This may give a feeling of fullness, pain and dulled hearing.
You can take a decongestant tablet with anti-inflammatory for a couple of days. Steam inhalation and yawning will help. If your still feel full, you can try to forcibly open your eustachian tubes by taking deep breath and blowing while pinching your nostril
and keeping mouth closed. If you feel a pop,means you have succeeded. If you feel dizzy while performing this, then stop and consult your ENT doctor.
Hope you found my response to your query informative and helpful.
With good wishes,
Dr.Chandra Shekhar Sharma