And to add to the confusion . . .
You probably had an increase in adrenaline while skiing. Adrenaline "potentiates" acetylcholine, meaning it increases it. While that may have been good for your MG it may have been bad for your heart. The articles out there are complicated but here are some anyway.
http://www.madsci.org/posts/archives...0695.Bc.r.html
http://www.ncbi.nlm.nih.gov/pubmed/2427705
http://jp.physoc.org/content/101/2/224.full.pdf
http://www.sciencedirect.com/science...27f74885328555
This only makes me believe more that you need a full cardiac workup, including perhaps ultrasounds of the main arteries of the head like the carotid (due to the headaches).
Annie