Hi--I was just wondering the same thing. I went to the lake a few times, and even though the day wasn't hot, and even though I sat in the shade the whole time, it did me in. I think that especially near a lake, there's so much reflected sunlight that sitting in the shade isn't enough.

Everyone will tell you that the heat is bad for MG. I think it's because in the heat (and the cold) your body produces extra acetylcholinesterase (the chemical that breaks down acetylcholine. In other words, heat is the opposite of Mestinon). But for me the problem seems to be not so much the heat as the sunshine.

Abby