When I was in Grade 2 I had trouble focusing in class - they brought in an audiologist to see if I had trouble hearing. They were surprised that no, in fact, I could hear extremely well - however they didn't recognize that as a problem, hypersensitive hearing.
A standard audiogram only checks to see that you can hear well enough in each ear, at different frequencies, say at 15 decibels. Checking for imbalances they check instead for HOW LOW of a decibel you can hear at different frequencies. Say in your right ear the lowest you can hear 1000 Hz frequency is 15 decibels, but in your left ear you hear at 10 decibels - that would show an imbalance by 5 decibels. Very few audiologists do this test, so I'd be very surprised if you found stumbled into one who did check it in this way.
Do you remember having ear infections as a child, and were they painful at all?
Re: Falling asleep - what you've said regarding sleep is another proof point to me that you likely have a hearing imbalance. I found the comment on HN I made going into more detail on theory of how it works - https://news.ycombinator.com/item?id=13657973 - and in it I explain why your brain may not be able to actually stop paying attention to sound, which of course - a natural cycle of falling asleep - will have your senses slowly diminish until you're asleep and not not getting strong signals from them, or rather not reacting to them - making it difficult to fall asleep.