Giardia lamblia and blastocysts hominis.
Giardia is nearly a sure “present” you will bring back with you if you visit India but not only India. It can cause light to sever problems [not life threatening], mostly diarrhea , abdominal pain and weightless. There is really no need for a potential toxic treatment like Flagyl. If doctors want to give a drug already then tinidazole is far preferable!!
Treatment for blastocyst-if necessary- is not easy. But also here herbal treatment will do well. The simplest treatment for both these parasites is probably : Garlic, but there are more options.
After treatment of giardia one should avoid for quite a while any lactose as this can cause a long term malabsorption with vitamin deficiencies especially vitamin A and zinc. Consult a doctor with experience in this field