Back Shoulder Blade Pain

I'm a 63 year old woman , Healthy  with the exception of Lots of problems with Sciatica pain latly. I've seen a chiropractor and it's helped. But for quite a long time I've had this strange pain Under my left Shoulder blade. This occurs only when I'm lying down on a hard chair. A dentist chair or Chiropractor table for example.. It doesn't start right away but if I'm lying too long It feels like a muscle that radiates from my back to the front under my breast.  much like a spasm. Once I'm up from the table the pain goes away.
I mentioned this to my chiropractor and he thought it might be gall bladder. Should I worry about this ?
Thanks