How do you know if the reduction of hearing in one ear is temporary?

This is about a15 yr. old, if that means anything. This is not about gradual hearing loss, but a sudden reduction one day, no pain, after few weeks it comes back.

What helps the doctor determine it’s temporary, and tell you to just wait for x period of time, etc., instead of deciding on a hearing aide, or something else? And what is the something else?
How does a parent decide to wait it out before going to the doctor or it will get worse if the visit to doctor is delayed?