SCboy,most probably you are HYPERventilated, not hypo.Sleep study and blood gases test may show that.Hyperventilation due to anxiety results in lowering CO2 in the blood. CO2 is in fact the component provoking you to breath. if CO2 is low, your breathing center just does not have enough excitation to control breathing rate and you feel heaviness in the chest, hypoxia etc. people with anxiety hyperventialktion complain for fatigue, chronic yawning etc.There are quite a chances that your sleep study will show increased physiological central apnea during falling asleep. This is also a sign of hyperventialtion. many of our fellows reported such finding and some of them were scared to death becasues nobody explained them that increased central apnea interval is a result of low CO2 in the blood which is not high enough to excite breathing center during transition from wake to sleep and back.That is why our fellows often report scary episodes (I had one too) when you wake up really unable to breath or wake up with a true feeling of an elefant sitting on your chest.usually this is releived either wil lowering anxiety, or with breathing tecniques or with the good help of CPAP.I had read recently a report about an old lady who was enable to sleep, and no medications could help her except really a bull dose of some mighty sedatives. She had to undergo a sleep test study and it was found she had over 350 epidoses of apnea in 8 hours!!!!!!!! CPAP cured her in two weeks completely.People who have central apnea due to MND usually do not have that as a separate syndrom - they demonstrate also a lot of other neurological changes. Most of them are of bulbar nature due to co-location of bulbar structures and breathing center in the medullar part of the brain (that is why bulbar onset usually kills far more quiclky than limb one). So your doctor really should not test your diaphragm provided your rib muscles and bulbar area (bulbar zone in the brain is also responsible for breathing activity, in fact our breathing control center is located there) did not show any signs of degeneratiove process.So please consider this, and maybe it would help a bit to relieve your fears.