ProAgonist,

You said "That sounds scary, so how much do you think I should wait? As I mentioned, symptoms can return after heavy physical activity, even if you feel fine. So how do I know in 2 months from now if I can go to that field trip or not?"

I suggested that you have 2 months to start being physically active. Start now with simple walks then progress to more strenuous walks or hikes. It symptoms manifest from the hikes, slow down. You can only find your tolerance for activity by doing it. Nobody can predict your tolerance.