I had a pretty worrying situation at both my NATS and CAA medical. I had no idea before hand but it became apparent thay I have a pretty shoddy right ear, well atleast in comparison with my left.
However I got through both medicals with both telling me i was pretty much "on the limit" (probably thanks to my love of rock music).
FYI, in my right ear I had 20 db hearing loss at 500, 1k and 2kHz.
Good luck!