Otitis media is also known as an infection of the middle ear. When fluid is involved, it becomes known as serous otitis media, also known as otitis media with effusion or fluid in the ears. This situation occurs after an ear infection. Fluid and mucus collect inside the ear, causing muffled hearing, along with a feeling of fullness in the ears. Serous otitis media usually resolves on its own within one to three months, however, if it continues past this time, treatment may be necessary.