failure of the eustachian tube to close
Well, to be most accurate: failure of Eustachian tube to OPEN. As you probably read, the tube connects the outside atmosphere via an opening inside the nose to the otherwise-sealed middle ear cavity on the other side of the ear drum. "Clearing" or "Valsalva" maneuvers such as yawning or chewing gum pull apart the soft tissue walls of the tube and allow air pressure to equalize in the middle ear to the ambient atmospheric pressure. Pilots and divers are pros at these maneuvers, but airline passengers must equalize as well.
If the pressure differential is rapidly changing and continuing equalization does not occur (say, while asleep!), then at a certain differential pressure the Eustachian tube will seal shut. Now the ear drum bows either in or out in response to the pressure differential across it and this stretching is very painful! Ear block. The reason babies cry on airplanes during descent. The pressure in middle ear gradually equalizes through tissue out- or in-gassing, but there may be hemorrhage on the ear drum or in the middle ear, and fluid can accumulate in the middle ear. For acute treatment, an ENT doc has an air gizmo called a Politizer that forces air into the nose and may match the pressure in the middle ear, force the Eustachian tube open, and allow the middle ear to equalize with the ambient pressure.
But what you are experiencing is transient Eustachian tube dysfunction. You can try an oral decongestant such as pseudoephedrine, or nasal spray such as oxymetazoline (for a few days only--chronic use will give you a rebound perpetual runny nose). But the more effective treatment is a steroid nasal spray such as fluticasone prescribed by an ENT.
While Eustachian tube dysfunction is increasingly prevalent as adults age, there may also be a more sinister cause such as tumor. With new onset of this condition, I'd strongly recommend you visit an ENT for a one-time evaluation, and prescription medication as needed.
And, as mentioned, heavy ear wax (cerumen) impaction which seals the outside ear canal may also cause a kind of external ear block and pain from a stretched ear drum. Of course, an ENT will treat this as well.
I've used pain as the most common symptom of these conditions, but distortion of hearing certainly occurs as well such as you report.