Why do I have sudden significant hearing loss in only one ear and what can/should I do about it?

You should see a physician immediately! Ear-Nose-and Throat Surgeons (ENTs, or otolaryngologists) are the most qualified specialists to help you with this problem, but this is definitely something that needs to be addressed as soon as possible. Acute hearing loss is a problem that can be best treated in the moment, and if too much time passes, there is a chance that the problem might not be able to be reversed. Without knowing too much about your specific story, there are several things that can cause hearing loss acutely after trauma. Damage to the nerve is one of the more concerning issues, as swelling can compress the nerve and cause either short or long term damage. Damage to the part of the inner ear that receives sound is also a serious concern. Additionally, the tympanic membrane (eardrum) itself can be ruptured during trauma, which can cause sound to be muffled. Of all the problems, this would be the least problematic, as it can be readily repaired and often heals itself. The key is to talk to a qualified specialist very quickly to have the proper hearing tests, imaging, and physical exam so that anything that can be fixed, can be fixed. Please see an ENT as soon as possible.