it doesn’t clear by day 10, or if pain starts.
Rapid pressure changes during takeoff and landing can trap air in the middle ear, especially if you had congestion from a cold or allergies. This can lead to barotrauma (sometimes called “airplane ear”).
That blocked, muffled, “underwater” feeling after a flight is usually from trouble equalizing pressure in your middle ear. Most people clear it within a few hours or days. But when it lasts a full week, it’s worth paying attention.
A few days = common. One full week = time to check in with a doctor.