Any sudden weakness, whether that be in the legs or swallowing muscles or breathing muscles, is a sign that MG is rapidly getting worse. Right before my crisis, I had sudden episodes of breathing weakness where it felt like I was going to stop breathing.

Other "warning" signs of MG getting worse would be things like chest wall muscles cramping/spasming because they are so weak. Or generalized weakness increasing.

Any one-sided weakness should prompt an exam by a doctor because it may not be MG. It can be a lot of things like a TIA, stroke in progress, etc.

So, in case I wasn't being clear because I'm so frickin' exhausted tonight, MG warning signs mean that MG is getting worse, possibly to the point of heading towards a crisis. At the very least, an exacerbation.

Just take it easy and call someone to be sure.