Do you feel sad during the winter months？If so，you might have seasonal affective disorder （SAD）（季節(jié)性情緒失調(diào)）.
    SAD usually starts in autumn or winter and ends in spring or early summer.As the weather gets colder，you feel more tired，sleepy and even hopeless.When spring returns，you may become well again.
    However，we still don't know the exact reason of SAD.Some scientists think that hormone changes can cause that.During winter，it stays dark outside for much of the day.That causes the brain to make more melatonin（褪黑素）.The melatonin makes you feel sleepy and less excited.
    Getting more sunlight（ 日光） is the best way to deal with SAD.Doctors say people should spend at least some time outside every day during the winter.But if you feel deeply unhappy，you should go to a doctor.

（1）When does SAD usually start？ （ no more than 4 words）

In autumn or winter .

In autumn or winter .

（2）Do we know the exact reason of SAD？ （ no more than 3 words）

No，we don't.

No，we don't.

（3）How does melatonin make you feel？ （ no more than 4 words ）

Sleepy and less excited.

Sleepy and less excited.

（4）What is the best way to deal with SAD？ （ no more than 3 words ）

Getting more sunlight .

Getting more sunlight .

（5）What should you do if you feel deeply unhappy？ （ no more than 6 words）

I should go to a doctor.

I should go to a doctor.