The flu can make chronic health problems worse. For example, people with asthma may experience asthma attacks while they have flu, and people with chronic congestive heart failure or diabetes may have worsening of this condition that is triggered by the flu. On the other hand, any otherwise healthy person can under some conditions develop complications from flu. It is very sensible to consult a doctor if any of the following problems appear: fever lasting more than 3 -4 days, deterioration of cough and chest pains, difficulties breathing, expectoration of greenish sputum, severe headache or ear ache, any other deteriorating symptoms as stomach pains, vomiting, diarrhea, skin rash etc.