I have to disclose that I am not diagnosing or attempting to diagnose, treat, or cure any illness or disease in this response.
My first question would be "Why are you dehydrated?"
Second, "Can you deal metabolically with the sugar that is in Gatorade?"
Third, "Is this a chronic condition, or did you try and "train" without FIRST properly hydrating?"
Fourth, "Why are you 'pretty sure' that you are dehydrated?" In other words, what symptoms lead you to believe this?
There are more questions but, the reality is that you will need to make a choice based on the cause of the dehydration. Either one for the short term should work.