What is going on with my hearing?

Sorry to hear that you are having problems with your hearing. You mention that it is happening on the left side, and that it is relatively transient (meaning that it doesn't seem to last for a long time...at least as far as I can tell from what information you have given me). There are multiple questions that I would need to ask you in order to help determine what might be going on with your hearing. Obviously I can't examine your ear, or take a thorough history in this setting, so I recommend that you make an appointment with an otolaryngologist (aka ENT). An ENT will be able to examine your ear and tell you if there are any problems with the ear canal that might disrupt hearing (like a cerumen impaction), or tell you if there are any anatomic problems with the tympanic membrane (ear drum) or the middle ear as can be seen through the tympanic membrane. If there are no obvious anatomic abnormalities that can explain the hearing loss, your ENT will likely order an audiogram (hearing test) to determine if a hearing loss is present, and what type of hearing loss it is. Depending on the results of this, they may decide to pursue further work-up, but they will talk to you about that if the situation presents itself. I hope that this at least gives you the best place to start (with an ENT) to determine what might be going on with your hearing. Best of luck.