What are symptoms of being a little depressed vs. getting clinical depression?

Having a bad day: Usually doesn't involve physical signs of the physical illness called major depression. So you would not have sleep, appetite or energy changes.

Depressed: Sad affect versus neurovegetative signs/symptoms of clinical depression such as changes in energy/appetite/sleep, which interfere with daily functioning or cause significant distress.

Clinical Depression: Clinical depression is usually severe lasting for 2 weeks or more causing emotional distress and affecting ability to perform personal, social, work responsibilities. Mild depression may be occasional sadness during the day or week which goes away and does affect functioning much or cause significant distress.