Read the passage below and choose one correct answer for each question.

Headache is a very common disease. The symptoms of a headache are various. People may have pains only one side of the head. Sometimes when the pain goes away, the head is sore. People have a headache when they work too hard or they are too nervous about something. Medicine can help cure the disease but people usually have to do more than taking tablets. They can prevent headaches by changing their diets or their lifestyles or simply by going to bed.

When do people have a headache?