"Sadness is different than depression Sadness a part of every human and animal whereas, depression is not a part of every human and animal. Sadness is a basic emotion while, depression is a mental disorder. Sadness doesn't lead to fatigue whereas, depression leads to fatigue. Sadness is short term, depression is long term. Sadness may or may not lead to loss of appetite or increase in appetite and insomnia or hypersomnia whereas depression surely leads to loss of appetite and insomnia (in cases of atypical depression it leads to increased appetite and hypersomnia. Sadness doesn't bring any changes in the body weight , whereas depression leads to weight gain or weight loss Sadness might include suicidal ideations but in depression a person who might have suicidal ideation is at a higher risk of commiting suicide. -Ashmi Makhecha"