Does seasonal affective disorder usually cause many symptoms?

Yes: Sad is technically a variant of major depression, so has all the associated symptoms of depression but with a seasonal pattern. This is usually depression in winter months which correlates more with length of daylight more than temp. Less common is a reverse sad, worse in summer correlating with temp. Many people have mild sad symptoms but don't meet criteria for full depression.

SAD Sx's: Depends on severity. SAD symptoms occur with change in season (often fall and winter) & can include carbohydrate craving, increased appetite with weight gain, low energy level, irritability, moodiness, sleeping more, heavy feeling in extremities, being overly sensitive to rejection and it can impact relationships.