Awww, B2Y, I'm so sorry.

I know it was something you loved doing...and hubby's right - maybe you just need a break until you retire (not that far away, ya know). It might just make the job of actually getting to retirement easier for you. Then...once you have time during the week to relax and rest up you can be refreshed and ready to go on Sunday.
Everything happens for a reason - I know you probably don't want to hear things like that right now - but I fully believe that you need to listen to your body and not push things to the limit.
Nobody is saying you can't
ever play the organ again. You just need to give yourself a break - and take the time to actually "go" to church again, and listen to the sermon without being in pain, and enjoy listening to someone else get the blessing of being able to play.