Symptoms may include feeling tired or ill, excessive thirst, frequent urination, sudden weight loss etc. Yes, a fasting blood test for Blood Sugar would be elevated most likely if you have early onset diabetes.
I suspect you are right, your thirst is related to something else and it may just be one of the quirks of anxiety.
You said you are not dehydrated so that is not your problem. How about your meds.............anything there that would cause your sx?
Do discuss this concern with your Doctor at your appointment next month as it is good to just get it out there and then if there is not a problem you can just stay in the moment and let go of the concern.
Happy Holidays to you,