[Kars]

A bowl of cold water with just your face in will do Brian. It's the temperture difference of your bodytemperture and the water that helps to generate a powerfull diving response. The receptors are all over our faces.

On your back condition, it sounds really mysterous. I must confess that I couldn't really understand from your initial posts what your goal and motivation is. Being weary of those young -I want quick tricks- for big results now, I started to develop a suspicion.

I guess you've tried many ways of elevating those pains. Stories like these make me feel very fortunate there is not much wrong with me yet, knokking on wood.
Appart from having a distractions, have you tried (self) hypnosis for relaxation?
There are some yogi techniques to stretch the diafragm, have you tried any?
I've also heart of yogi exersizes in short breathing, meaning they try to have as little ventilation as possible not moving a leaf of paper hanging just before their nose and mouth. Breathing shallow trough the nose laying in water helps me to relax me and preapair for that 1 big static I do without any breathholding in my preperation.

Warm water also helps to prevent contracions, 34 c I like.
Also a flexible diafragm allows easyer contractions.

If you got a knowledgeble and capeble buddy for safety you can try some diafragm stretches in warm water by doing frc and emptier dives to the pool bottom.

I find doing such dives to 5m (~16ft) with a divetime of 1'45" invokes a great DR, bloodshift, and makes me feel very relaxed, though also a bit tired in an energetic way. Usually I wear a suit fins and noseclip, to keep my muscles warm and flexible and to expose my face to the 26c water. with a gradual diminishing amounts of air I go down slow, eyes closed, sit at the bottem for 30s and very slowly fin up. Upon surfacing I breath in slowly, in parts, as I want to allow my lungs to shrink and expand gradually.
This exersize puts pressure on ribcage, diafragm, heart, throught, so maybe not your thing.

Love, courage and water!

Kars