I have a similar situation, but I think I have resolved it with my neuro (finally!).

I easily get overdose symptoms from Mestinon and this gives me nervousness, tense muscles and double vision. My neuro originally told me the same thing as what you said, to take Mestinon whether I have symptoms or not...I had to keep complaining to get my Neuro to finally let me vary my dosage somewhat within a certain agreed upon range and I am doing much better now.

I do try to keep at a steady dose, but this stupid MG is not consistant for me...I can go a few months at one regular dosage and then suddenly, in one day, my symptoms get worse or better (which is actually more scary for me than when the MG symptoms worsen, I don't like the Mestinon overdose symptoms) and I need to change my Mestinon schedule immediately or the MG (or the overdose symptoms) gets worse. It is scary for me when my MG symptoms change, I don't understand what makes it happen so suddenly but it does seem to be somewhat related to what I eat, my emotions and chemical exposures. I am trying very hard to avoid stress, to eat good foods and avoid chemical exposures.

I do have to take Mestinon or I get so weak I can't function.

Right now I am taking 30 mg of Mestinon in the morning, and then I take 15 mg 2 or 3 times throughout the day for a total of 60 to 75 mg total in a day.

For a while I was taking only 15 mg of Mestinon every day to keep my MG symptoms almost gone but that only lasted a few months.

You know your body best. Keep giving feedback to your neuro. I found that my neuro gave in to letting me vary my dosage when I started calling his office every time I thought I was getting overdose symptoms.

I hope this helps