school trip

Hi,  my son is 11 and has an ASD. He is currently on a school trip for the week. He went off fine yesterday and was very quiet which is unlike him but he seemed to be happy to go. I received a phone call this morning from his teacher to say he was complaining of tummy upset and that he didnt get to sleep until after midnight, the teacher said she thought it was anxiety.  I believe it is part of his anxieties which do happen a lot. I keep thinking about him and now wondering if I made the right decision to let him go. He really did want to go. I would be grateful if anyone has any advice.