You can become sad when you lose your job, lose a family pet, or when you experience a death in the family. It is very normal to feel this way. The sadness that you experience will often be immediate but you are able to continue on with your daily routine, such as getting up out of bed and going to work or school and taking care of your family. Usually through time the sadness will slowly reside, depending on the individual and you continue forward.
However depression is more chronic. Depression is more than just feeling sad. Depression may begin with a sad mood such as those mentioned above, but the sadness lasts for a long time and begins to interfere with your normal everyday daily functioning. For example, you may not want to get out of bed or have the energy to take a shower. You may want to isolate and not interact with anybody or lose interest in activities that used to be fun. You are crying for no reason at all and feeling sad all the time. You may feel irritable and are easily frustrated or restless. You have trouble falling asleep or staying asleep or you sleep too much. You may also have a loss of appetite or are eating when your’e not even hungry. Physically you may experience aches, tension, headaches, stomach pains etc. Having difficulty concentrating, remember details or making decisions is another symptom of depression and you may feel fatigued and tired all the time. Feeling guilty, worthless or helpless and having low self-esteem is common and some people may experience having thoughts of suicide or hurting oneself.
For more information or some tips on how to cope with depression, you can read the article ‘What is Depression?‘ by the American Psychiatric Association