I'm feeling symptoms of depression.i cry for no reason and feel worthless. i often think of death.but sometimes i feel confident &ontop of the world.

Bipolar: You should be evaluated for simple depression versus possible bipolar or manic depressive disorder

Possible Cyclical DO: You, may be describing a cyclical mood disorder: of which, bipolar disorder has the symptoms you describe. If there is a family history of depression, bipolar disorder, this increases the chance of having bipolar disorder. But, you need to see a psychiatrist to make a correct diagnosis, and for appropriate treatment.