When I was at my worst mentally I had a lot of weird physical symptoms as well. The fact my depression wasn't being managed even by a sledgehammer attack of 3 different drugs all on top of each other implied there was probably some sort of physical cause. So I went off and had blood tests for just about every medical condition that can cause depression along with fatigue and body pain. Everything came back negative - to the surprise of my GP. It was all quite confusing. It was only when I got really really physically sick, and became too tired and weak even to be able to walk, and finally dragged myself into the doctor with a complete list of every single symptom I had that the answer turned up. And it was surprisingly simple. "Hyperventilation occulta", my doctor said. WHAT?!
It turned out that almost everything I was experiencing was being caused by one thing: bad breathing. In this modern day & age, where asthma gets treated by shoving a couple of inhalers at a kid, very few doctors or nurses take the time to actually check how the patient is breathing. On reading up about it and going to see a specialist physiotherapist, the problem became even clearer. It transpired that I had probably never used my diaphragm properly to breathe, and had only ever breathed using the accessory muscles in the chest and (during asthma attacks) the neck and shoulders. It also transpired that I breathed with my nose and mouth together, at a rate roughly 4 times faster than normal. Um.
Apparently the carbon dioxide level of the blood is very important in a number of regulatory processes. It controls how much oxygen you breathe in, for starters. It is also involved in such diverse things as temperature regulation and the production of adrenaline. And the brain, or hypothalmus, works assuming that the baseline carbon dioxide level of your blood is normal. If, over a long period of time, you breathe out too much carbon dioxide, the baseline gradually drifts lower and lower, and your body forgets where "normal" really is. The upshot of this includes such delights as exhaustion, muscle weakness, depression and panic attacks. Really.
Anyone who's had an anxiety disorder knows that panic attacks breed panic attacks. You have one, and you're likely to have a bunch more in quick succession. Quite apart from the underlying stresses which feed the anxiety (and then the fear of breaking down again which makes you all the more likely to), there are the physical symptoms of panic attacks which lower your blood carbon dioxide level, boosting your adrenaline level and making you into a giant timebomb. Panicky people tend to breathe quickly, and may even hyperventilate enough to notice. Their heartbeat speeds up. They sigh, or gasp. All things that mess up how much CO2 is in the blood.
I have had a cold for a week, and my nose has been blocked for much of this time. I have been forced to breathe through my mouth a lot, with much sneezing and coughing. It is not, perhaps, surprising that I woke up today in that waking up from a nightmare panicky can't cope shit gonna die what? exhausted need more sleep rinse repeat cycle that I know and love from my past.
What is surprising is that I didn't recognise it, until I had a complete meltdown just now.