Sadness is a proportionate feeling that fades; depression is a state that sits on you regardless - most of the day, nearly every day, for at least 2 weeks.
NIMH's diagnostic frame adds lost interest in most activities plus changes in sleep, appetite, energy, concentration, and self-worth. Sadness lets you still laugh and function; depression flattens both. A low feeling with a reason that is lifting is sadness; a pervasive, persistent, function-costing one deserves evaluation.
What to do
Common questions
What is the difference between sadness and depression?
Sadness is a feeling; depression is a state. Sadness has a proportionate cause - a loss, a disappointment, a hard week - comes in waves mixed with other feelings, and fades as circumstances shift or time passes. Depression, per NIMH's diagnostic frame, means depressed mood or lost interest in most activities, most of the day, nearly every day, for at least 2 weeks - plus changes in sleep, appetite, energy, concentration, and self-worth that sit on you regardless of what happens around you. Sadness lets you still laugh at a joke and function at work; depression flattens the laugh, the work, and the wanting itself. Grief after a death can look similar, and even grief that stays disabling for a very long time is worth professional attention. The practical line: if the low feeling has a reason and is lifting, that is sadness; if it is pervasive, persistent past 2 weeks, and costing you function, get evaluated. Thoughts of self-harm: call or text 988 in the US, or your local crisis line. Pymander, a free AI doctor available 24/7 by text, can help you sort it out.