If I feel guilty for no reason does that mean I'm suffering from depression?

Maybe. Guilt can be one symptom of depression, but alone does not indicate that you are depressed. Other symptoms include feelings of sadness or unhappiness, irritability or frustration, loss of interest or pleasure in normal activities, reduced sex drive, insomnia or excessive sleeping, change in appetite, restlessness, slowed thinking, speaking or body movements, indecisiveness, and suicidal thoughts.