Luke, I started reading Claire Weekes and ran into the following:
"THE SHOCK OF WAKING
Also a sensitized body can react to the slightest shock. Even the mild shock of waking from sleep can make a heart race. "
...
(and somewhere else)
" I have sometimes been surprised at how quickly a patient can recover from shallow breathing when he loses fear of it...... do not be disappointed if, despite understanding, you still have occasional difficulty in breathing deeply. It is not important. Acceptance (real acceptance) once more works the miracle by releasing tension."
Breaking the fear and the constant focus on your breathing is key for you. Do you ever experience not breathing shallow after a period of not focussing on it? If so, you know it is TMS. The respiratoy centre of your brain automatically regulates your breathing in a near perfect way. If it wouldn't, how would you breath while sleeping?
I suggest her book "Essential help for your nerves". It is the only book I purchased besides Healing back pain. It also sheds some light on the fatigue you talk about.