The flu and the common cold are both respiratory illnesses with often similar symptoms.  In general, the flu will make you feel worse than the common cold, and symptoms such as fever, body aches, extreme tiredness, and dry cough are more common and intense with the flu.

Colds generally do not result in serious health problems, such as pneumonia, bacterial infections, or hospitalizations. Although for most people any kind of flu will simply cause nothing worse than several days of misery, especially for those at high risk it is more likely than a cold to develop into a more serious respiratory illness, including pneumonia and other serious bacterial infections.

Because it is sometimes difficult to tell the difference between a cold and the flu, here are some warning signs to watch for, courtesy of the Centers For Disease Control (CDC). If someone with bad cold or flu-like symptoms develops any of these signs, it's time to get medical advice right away:

Difficulty breathing

Fast, shallow breathing

Rapid pulse

Chest pain

Blue or purple lips or skin around the mouth

Fever over 101 degrees for more than 24 hours

Repeated vomiting and diarrhea

Seizures or convulsions

Signs of dehydration: Uncharacteristic mental confusion, decreased urination, dizziness

Those at high risk for complications from the flu, including those with chronic illnesses, those with immune deficiencies, pregnant women, children, and those over 65 should not wait to call their doctor for instructions if they believe they have the flu.

If you are concerned about the symptoms you see and you are coming up to a weekend, don't wait to call the doctor. If you wait you may be looking at a weekend trip to the emergency room, which you want to avoid if at all possible. However, if you can't reach the doctor, and you are concerned about the condition of your person with the flu, it is better to make the trip. Someone who is having difficulty breathing can run into serious trouble very quickly.