Chronic Pain & Anxiety - peptide neurotransmitter link
 

Bumping up this interesting article from Neurotalk's sister site PsychCentral, about chronic pain and anxiety being connected :

Chronic Pain and Anxiety Linked By Neurotransmitter | Psych Central News

The article is brief in detail but further research of the term "pituitary adenylate cyclase activating polypeptide" leads to more information on how widely this neurotransmitter can affect the body. Here's a couple of links to relevant abstracts but there's more out there:

Pituitary adenylate cyclase-activating polypeptide and its receptors: 2 years after the discovery. - PubMed - NCBI

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily. - PubMed - NCBI

Anxiety and side effects
 

Anxiety sometimes goes with chronic pain. If medical CBDs in legal in your state you can try these before medications or after if you have too many side effects.
I am one of those people that cannot take anxiety mess because of side effects and this has helped me.

If people would be more MINDFUL of breathing and relaxing body, pain would lessen. Even relaxing shoulders if you think of it helps. I just relaxed my shoulders and a lot of pain left my joints.

The PT's in the rehabs I just came out of, 3 of them for knee issue, kept saying BREATH...

I don't live with chronic pain but sometimes have anxiety/panic attacks.

Deep breathing helps with those for me.

There is a good physiological reason for this. Sometimes an anxiety/panic attack leads to fast/shallow breathing which can lead to a build-up of CO2 in the blood.

Doing slow/deep breathing for about 15 minutes or so works for me.

Slow deep breathing does bump up oxygen in blood, no doubt.