I'm having such a terrible day

My son is ten, autistic and severe learning difficulties. He went off on his very first residential school trip this morning. All I've done since is cry. First I cried because he doesn't understand properly what's happening because of his difficulties even though i'm assured he'll love it and I know he will. Then I started crying this afteroon when I heard the forecast for tomorrow is heavy rain and more rain. I have the timetable for the school trip and they had planned to go to a local theme park, persumably with tickets. I am totally distraught that this will not happen due to the rain. I haven't been able to stop crying for several hours now and I'm really worked up. I can't explain why I feel so awful. My son wouldn't know he had missed it. I just can't stop thinking about how much he would have loved the theme park and he can't go because of the horrible weather. Plus most of the activities where they're staying are outdoor ones.

I have been crying to the point of hysteria and I don't know what is wrong with me. I feel like everything has gone wrong and I'm on complete meltdown.

Is it normal to be this upset? Is this related to my childhood? I don't know what to do.