A similar thing happened to me - I was finally diagnosed in September last year and put on 60mg 4 x per day of mestinon and it was great! I was able to build up my activity level and was finally able to do more than just barely make it through a morning at work and spend the rest of the time completely worn out!! Then, in December we had a trip to Disney booked which we had planned a year earlier and those 4 little days have thrown everything!! I have not been able to get back on an even keel since!! My mestinon is now less effective and it's effects more intermittent and unreliable, My dose was increased to 90mg 4/5 x per day but I spent 3 weeks getting rapidly worse and having chest heaviness/pressure (especially when standing) on that dose so I have reduced it back to the 60mg again while I wait to see my Neuro again....which isn't for another 8 weeks!

I'm afraid I don't know the answer to your question as to whether this means the illness is getting worse or I wondered whether we can get used to the mestinon (some quicker than others in our case!) and the effects reduce when that happens?! I know other illnesses can put our immune system to work which in turn is not good for MG and I did speak to my Neuro's registrar when I was really worried about my breathing last week and she said I shouldn't blame the trip to Disney, it's my immune system at fault and overdoing things is one of the worst triggers for Myasthenia so perhaps your knee put extra strain on your body as the trip did for me and that's why we're in this situation?

I look forward to seeing what others say here and wish you all the best - I hope you are able to feel better very soon