Is this really an MCAT question? Aldosterone does a bunch of things, but basically in the collecting duct of the kidney haa a net effect of favoring sodium reabsorpton and potassium secretion. This is all part of a system to help regulate volume status as well as electrolyte concentrations, which im sure you know. Essentially, the absorbed sodium will drag water along with it (which is the main purpose of sodium reabsorpton here), which will dilute sodium to an extent, and there exists other mechanisms (ADH, ANP, etc...) which help to further regulate sodium and bring it back to normal. Potassium on the other hand, will be abnormally low, so this person in your question is quite likely to be hypokalemic without necessarily being hypernatremic. Hypokalemia in general causes increased flow of potassium out of the cell which decreases the resting membrane potential, making firing an action potential more difficult. At a muscle, this will cause weakness. Derangements of other ions will also affect this finely-tuned process. Read about hypocalcemia, hypercalcemia, and hypomagnesemia as well, which along with others may also cause similar neuromuscular symptoms (weakness, tetany, seizure, lethargy, paraesthesias, etc...)
