HI Well come to HCM I really appreciate your concern, the reason of gastritis and the acid peptic disease with ulcer formation could be due to NSAID and it is not the high altitude flying, but it can be managed successfully with particular drug like proton pump inhibitor, and it has to be taken for at least six weeks, there should be some restriction as long as diet is concern, in another word life style change is necessary along with medicine, try to avoid spicy, oily food, avoid heavy meal, stop taking alcohol, smoking, coffee prior to bed, stay away from stress, it is better to stop taking NSAID now, hope this information helps.