Hi,
Pain due to deep breathing does not indicate GERD.
It could be due to musculoskeletal cause ( there are other causes as well). Take a dose of tylenol if it occurs again.
If it does not get relieved with tylenol, then get examined by your doctor.
Beth, i have the same symptoms for about 2 months now. I am going in for an endoscopy this week to see if I have GERD. But ya I have the same knot, or pain when I get up. Seems better as i walk around and can feel it when i'm sitting at my desk. My GP told me to lay off working out for 3 weeks, just light 10 minute stuff. So I've been doing stretches to help stretch the chest. Not sure its having much effect. He thinks is muscle related or GERD related. When you google it, there are 100's of causes, including hiatal hernia, ulcers. I can tell you, its just plain miserable. Let me know what you find out. Hope we all get better soon!