I have had enough experience with Mestinon at this point that I am allowed to adjust my dose as needed. I first started with 60 mgs every 4-6 hours as needed. If I didn't feel a good amount of relief, I called my neuro and she would tell me how I could adjust. At this point, because I know the fluctuations I take it more on an as needed basis, 1/2 to 1 at a time. Some days, I don't need any. Other days I'm taking it every 2 hours.
When in doubt, I take just a 1/2, then another 1/2 if I am not getting enough relief within 30 minutes.
The symptoms of too much Mestinon are much the same as not enough, except in addition to weakness I notice increased persperation and muscle twitching. If you have started other meds, like steroid or immune modulating therapy, the amount of Mestinon you take will probably decrease as those start to build up and work in your system, so it can be an ever changing limit on the Mestinon.
You really should talk to your doctor to get better guidelines of how you should take it to determine your correct level. Your doc should have an idea of what level of weakness you are at, and really would be the best to advise you how to build up to your best dosage schedule. I would call them right away and tell them you need more direction.