I have lost about 10 lbs in 6 days while having stomach flu, which i still have. is this normal?

Can happen: You can lose excess fluids through diarrhea and vomiting. If you are taking in few calories - you may be burning up glycogen which is stored in the liver. That also holds fluid - so can lose more fluids that way. In addition - you may be burning some muscle and fat. Ensure that you hydrate well. If you can't keep up with fluid losses IV hydration may be needed.