Not usually, due to emotional involvement. Depression is often masked by anger, loneliness, compulsiveness. It often takes the informed probing of another person to reveal depression. Persons who are repeatedly depressed can learn to recognize its signs. Many do not realize that they are suffering from depression.
Mild depression is difficult to gauge.
Serious depression prevents rational analysis. Mild depression is tolerable and we can function fairly normally with it 2. Medium depression begins to affect us. We begin getting out of obligations. Severe depression blocks us from eating, deciding, caring for ourselves.