You don't have to stop yourself from feeling sad sometimes. Sad is good. A full range of emotions is healthy. Bereft, melancholy, miserable, grief-stricken – these are all important feelings. Feel them.

Depression is not sadness, it's misery unrelated to your situation, or often a lack of feeling, altogether.

If you feel you're sad all the time, or over a long period of time, or if feeling down is interfering with living your life (going to work or school, grocery shopping, paying your bills) – that's when it's time to seek help.