It's caused by softened wax against the eardrum (usually softened by water). It should eventually pass, but you should be able to get some eardrops from a pharmacist to speed the process.
I get it quite frequently, very annoying. Just don't stick anything in your ear - this is tempting but can cause:
a) otitis (inflammation and infection of the outer ear - requires antibiotics)
b) packing the wax more tightly against your eardrum - uncomfortable
c) damage to the eardrum - very painful and potential permanent hearing damage
d) getting something else stuck in your ear - requiring an embarassing trip to your doctor
So resist the temptation to remove the wax physically.
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Time is an illusion. Lunchtime doubly so.
Epona of The Laughing Hyenas