Negative middle ear pressure occurs when the Eustachian tube between the middle ear and the throat gets blocked. The ear absorbs all the available air, thus creating a vacuum. This leads to retraction (sucking in) of the eardrum, which in turn can lead to hearing loss or tinnitus (a ringing in the ears). The vacuum may draw fluid from the mucus membrane of the middle ear, adding to the hearing impairment.
See an ear, nose, and throat doctor (otolaryngologist), preferably a surgeon, since the problem may eventually entail an insertion of tubes to remove fluid build-up.
Take any antibiotics that the doctor prescribes to completion. This is to address any infection that is causing the Eustachian tube to inflame or clog.
Consider surgery for insertion of tubes to clear out any fluid that remains after a round of antibiotics. This entails the surgeon's making a narrow incision in the eardrum, into which s/he would place the tube. This allows continual drainage.
Be sure that the fluid from the middle ear sampled during the surgery is examined in a lab to tailor antibiotics to the nature of the infection.
Use eardrops as directed. Avoid swimming underwater. Use earplugs while showering. Make sure any water that enters the ear eventually exits.
Allow 4 weeks after surgery for healing to complete. The tubes will fall out in 6 to12 months. According to EarSurgery.org, "In most patients who undergo this operation, the tubes are successful in preventing recurrent fluid."
Have the doctor check for a tumour if several rounds of antibiotics don't work. Tumours are rare, but then that keeps them from being checked for.
Since a mistake during tube insertion can be life-changing, try to find as qualified of a surgeon as you can. Attention to detail, board certification, and graduation from a top medical school are indirect indications of exceptional care in the operating room.