You sure the keyboard wasn't malfunctioning? Those floor models can get pretty beat up.
Otherwise, time to get the ol' hearing checked. Start taking precautions to save your hearing as well (ear plugs for loud noises, turn the music and tv down).
I've got some hearing loss in my left ear from too much loud music as a youngster. I try my best to make sure my kids don't have the same problem!
Guitars:
Fender 2006 MIM Fender Stratocaster HSS in 3TS
Ibanez RG 570 with a bridge Invader
ESP M II Deluxe with a Tune-o-Matic bridge
Eleanor, the magical, mystical Road Worn wonder Tele
Blackstar HT Club 40