I had this during my first year/two year Post accurate syndrome, it seems completely resolved now . I can't say for sure what did the trick but I know I eat more salt ( pink salt from Himalaya ) than before, less fruits, less liquid, carbs only at night after sports
Try to identify and avoid obvious causes - think about pesticides, chemicals, free radicals or nutrient deficiencies. Diabetics may get autonomic neuropathy because high blood sugar levels damage nerves.
Give your body time to adjust - don't jump up too quickly.
Work the muscles of your legs for a few seconds before standing up - this prevent blood pooling in legs as the muscles squeeze the blood out of the veins back to the heart.
I would treat postural hypotension as a sort of peripheral neuropathy and use high dose B vitamins and possibly vitamin B12 injections to encourage the nerves to heal and repair. I would also check DHEA levels on the grounds that this encourages repair of tissues.
Postural hypotension could be caused simply by low cardiac output. See Low cardiac output state. It is much easier for the heart to pump blood on the flat (lying down) than up and downs hills (standing up). Indeed we all feel more comfortable lying down or sitting rather than standing. In severe cases of chronic fatigue syndrome the heart is in a low output state, perhaps sufficiently so that it cannot pump enough blood round when standing. It can maintain blood pressure for a certain time, but then becomes fatigued and so the blood pressure falls. Clinically this is called Postural orthostatic tachycardia syndrome or POTs. The treatment of course is to treat the mitochondrial problem. See CFS - The Central Cause: Mitochondrial Failure.