Living Fully Nourished

A while ago, a person with celiac disease told me that while he was on holiday in a foreign country, he was forced to eat gluten and apparently it had not affected him. He asked me if he might have overcome his disease.
On another occasion, a celiac child’s mother told me that she was sure that while eating in restaurants during their holidays, her daughter had eaten traces of gluten, probably even in considerable amounts, however, she had suffered no effects. Meanwhile during the school period, any small contamination of gluten seriously affected her health.
In both cases my answer was that all this had happened due to the holiday effect!
Why do intolerances decrease while on holiday? Why several people feel like their disease has healed on holiday?