Hello, Thank you for the query and welcome to Healthcaremagic! In order to help you out i will need a some more information about your grandmother s health like since how many days is she having diarrhea?How many times in a day does she pass stools now? has the dizziness started after the diarrhea started? Is she a hypertensive patient? The cause of her dizziness can be many, but if it has started post her diarrhea condition and not adequate salt based liquid not given to her during her diarrhea , its likely her dizziness is related to fluid and salt loss from body. This can be dangerous especially in old patients. Thus advise to get her blood pressure and blood electrolytes checked to rule out salt loss as cause of her dizziness. Other causes can be low hemoglobin, infection, generalized weakness or high bp etc. Thus i would advise get her checked in local ER to rule out causes which will need hospital admission. Hope this was helpful. Follow back for any future query. Takecare!