Both viruses have similar, unpleasant symptoms. However, if it is flu you will probably also have aches and pains, feel hot and shivery and have a temperature - which may be quite high. Flu symptoms can last several days and it is important to take care of yourself by resting, drinking plenty of fluids and taking aspirin or paracetamol to reduce the temperature. Sometimes patients can feel tired after a bout of flu and take a little while to get back to normal. This is quite natural and you should not be alarmed by it, although of course the doctors will be happy to see you if you feel it is necessary.