Many people experience the feeling of ear blockage at some time in their lives. It is sometimes caused by the middle ear filling with fluid. This can happen due to infection. Even a mild infection like a common cold can be enough to block the Eustachian tube. This stops the ventilation of the middle ear. The air is absorbed and replaced by water which does not conduct sound well. This leads to a feeling of hearing being muffled. As it comes on quite quickly it is easily noticed.
Blockage from the build up of wax and dead skin can be less noticeable. This is mainly because it comes on gradually. Hearing may be muffled. Sometimes it might suddenly get worse when water goes in the ear because the wax can become waterlogged. This can lead to a sudden feeling of ear blockage.
Sometimes the ears feel blocked when you fly in a plane or climb a mountain. This happens when the Eustachian tube which connects the middle ear to the nasal passageways isn't opening properly. This can happen due to allergy, a cold or enlarged tonsils and adenoids. Sometimes there is no specific cause. As the pressure drops the eardrum is stretched. If the Eustachian tube allowed air into the middle ear it would equalise the pressure on both sides. Without this equalisation the eardrum becomes stretched. This stops it vibrating properly, reducing your hearing and making your ears feel blocked. Flying ear plugs can help by slowing the effect of the pressure on the drum.