Hello and Welcome to ‘Ask A Doctor’ service. I have gone through your query. I can understand your concern. From the description of your symptoms,i can deduct that your vitals (your blood pressure and your heart rate) are normal. It is evident that you had orthostatic hypotension that generaly happens when you stand up. For this problem my advice is to stand up very slowly (not immediately) and to increase a little bit your salt intake. About the diarrhea,i can say that this is a dangerous symptom in your circumstances because it can produce dehydration and precipitate an Addisionian crisis. In my opinion this this the cause of your actual weakness. In this cases it is recommended to increase the cortison dosis and to drink plently of liquids in order to avoid dehydration and the electrolite balance. If you feel that your are extremely weak ,i suggest to go to ER as soon as possible,because you may need urgent medical help. Hope this is helpful. Take care.