I found out about this brilliant diagnostic test, which one can actually do at home, while waiting for an appointment to get my ear sorted out, which is a bit blocked up right now. If you have hearing loss on one ear, strike a tuning fork and hold it against your skull along the symmetry line (actually, I put it between my front teeth, as I do when I use it for tuning), to make sure it is at equal distance from both ears.
If your hearing problem is due to sound conductance within the ear channel (as mine is), you will hear the vibration of the tuning fork louder in the affected ear than in the healthy one, so the sound seems to be coming from the affected side. Which is a bit surprising when you have spent days not hearing anything on that side.
If, by contrast there is a problem with the actual sensory mechanism (or further downstream), the affected ear will be dimmed as in all other hearing, so the sound seems to be coming from the healthy side.
Works really well, and it is kind of reassuring when you get the right result.
More about the Weber Test in Wikipedia