It depends on whether the flu is a respiratory flu, or "stomach flu". If it's respiratory, you have a high fever, you cough for weeks, and you feel absolutely horrible with aching and shivering. You can have hallucinatory dreams and a terrible headache. You literally can't get out of bed. It lasts at least a week. In "stomach flu", you will be vomiting every 10-15 minutes, you can't keep even liquids down, and you get dehydrated. You also have a high fever, headache, and you ache all over. Thankfully, the vomiting stops after about 24 hours. You can also have diarrhea with it. Neither kind is something you would want to have.