yep stress does cause us to excrete minerals like magnesium that help muscles function properly.
also yes coconut water is high in potassium which is needed for nerve function. magnesium is needed to utilize potassium.
interesting abstract excerpt:
Magnesium, Potassium and Zinc Deficiency in Subjects with Type II Diabetes Mellitus
Subjects with type II DM had lower concentrations of magnesium (3.79±0.32 vs. 4.29±0.22 mmol/100 g FFDS), potassium (40.5±5.17 vs. 46.1±3.81 mmol/100 g FFDS) and zinc (231±29 vs. 247±23 ng/mg FFDS) in skeletal muscle.
while i can't compare those skeletal muscle concentrations to serum numbers posted elsewhere, we can still see that the patients have lower levels than healthy controls.
ms patients are also lower in (serum) mag and zinc compared to healthy controls. i have not been able to find anything specific to suggest that ms patients are low in potassium. i can't find a decent case control study looking at serum potassium at all.
did find this in NEJM:
A low serum potassium concentration is perhaps the most common electrolyte abnormality encountered in clinical practice. When defined as a value of less than 3.6 mmol of potassium per liter, hypokalemia is found in over 20 percent of hospitalized patients.1 The majority of these patients have serum potassium concentrations between 3.0 and 3.5 mmol per liter, but as many as one quarter have values below 3.0 mmol per liter. .
as for supplements, i used to recommend natural calm but now i prefer magnesium glycinate. you can ingest more elemental magnesium in this supplemental form, without suffering negative GI effects.
magnesium is supposed to be absorbed in the lower intestine and the glycinate form, being chelated, has a better chance of doing so.
magnesium makes chlorophyll green. ergo dark leafy greens like swiss chard and spinach (boiled) are great dietary sources.