I was wondering the same - I was a concert once, and was putting in earplugs - when I noticed one ear wasn't affected as much as the other when I put the earplugs in.

Testing showed I had some hearing loss - but not a lot. I ended up getting more tests. They played a series of words into my "good" ear and I had to repeat them: "duck"... "duck". "concrete" .... "concrete"... it was pretty funny.

Then they did the same thing in my other ear: "schmwaaa" ... "Smchmwaa?"... "Grunnnngch"... "wtf?!". Turned out I had an accoustic neuroma - a tumor on the auditory nerve. Got it cut out with some neurosurgery, but now am 100% deaf in one ear with shitty tinnitus.

Hearing loss is pretty common so I don't want to scare-monger - but, OP - follow up on the tests!