Hello As you mentioned that you felt sick immediately after meal and there is fatigue , muscle cramps and excessive sweating . As this is a very complex phase because simple test (blood ) will not yield any result because all these symptoms , you mentioned in your query may be due to , these includes. 1 Hyponatremia or Hypernatremia , diagnosis can be confirmed by blood examination for sodium level at different stage because of excessive sweating ( day & night ). 2 Hypokalemia or hyperkalemia , diagnosis can be confirmed by blood examination for potassium level . 3 Hypovolemia , as this is most common cause in patient having such symptoms ,because due to excessive sweating there may be depletion of water volume in body essentially with the loss of sodium . As we don t know about your diet so very difficult to establish any diagnosis , so either upload all details about various elements in blood with water volume or else consult a physician ( 2nd) and get an examination of different anions & cations . Hope this information will help you. Good luck.