Many of us have experienced the symptoms you have had to suffer. I know well the ankle and shin pain, the fast heart-rate, the chest and breathing issues and I too was put on the non-pharmacological treatment for POTS (i.e salt, more fluids, support stockings, etc).
Tell me, have you ever had an MRI of your head and neck because I think that would be interesting, I think it would show maybe problems with a flattened pituitary and several other issues common to many of us. You may benefit from sleeping in a rigid collar (I prefer the Philadelphia collar) as this will help maintain a better flow of your Cerebro Spinal Fluid during the night, which should help alleviate any overnight build up of pressure and help your pituitary to recover.
I would suggest elevating the head of your bed too (if you’re not doing so already) or sleeping sitting up. I feel much better for sleeping sitting up. How well do you sleep ? Have you tried an abdominal binder, to help with the POTS symptoms ? It can help with your posture too, putting less strain on the spinal column.
Try and avoid doing tasks standing up, always find a seated way of carrying out your daily tasks wherever possible and try not to lift things from ground level, get used to putting things on the worktop or a small table, rather than the floor. If you’re working on a computer, make sure you look at the monitor straight ahead, raise it up to eye-level if you can, using a few thick books if necessary. Try and avoid working with your head down (in flexion).
Deficient collagen is a contributing factor for many of us too, so try and increase your vitamin C intake (several small amounts, whilst your eating, is better than one large amount by the way). Vitamin C is necessary to help the body make collagen. Also raw foods, such as a variety of salad items will help build up stores of any minerals lost (we can easily deplete minerals when our autonomic nervous systems aren’t working properly)- but remember to wash it well first, as we don’t want to risk eating any organo-phosphates, as this can affect us badly.
Hope some of this info proves helpful to you. I wish you well, lets hope this is the start of an improved life for you.
NOTE: I eventually tried the abdominal binder – not good for me, it slowed the transition of food through my bowel right down, so I don’t advise this.