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In all probability this is food poisoning. Take an OTC lactobacillus preparation and yoghurt with your meals. Drink plenty of fluids. Eat light, do not stay hungry but eat simple things like toast, porridge, cereals, crackers, banana, rice, peeled apple, etc. Take ORS. Take over the counter antacid and antiemetic (this SOS for vomiting). Watch out for a day or two with this treatment. If it does not help, consult a doctor immediately. Take care!