Well nausea is usually a sign of Food Poisoning or Gastric
Flu.
What u can do if not serious, is to buy some charcoal pills along
with the Mylanta. Charcoal absorbs any toxins present, while
Mylanta acts to relieve wind and acidity.
Drink plain water as much as u feel you can hold down. Stay away
from oily meals, fried foods, and spicy stuff. Go for porridge
instead of rice till you feel better.
Servere case of Food Poisoning will give you Fever with cold
shivers, constant vomiting and dairea, you feel dizzy all the time
and your stomach and lower abdomen aches like hell. This would
warrant a visit to the hospital.