How could i tell if someone's depression has come back?

Depression relapse: The first thing i would do is ask the person. I would also observe for the symptoms of depression: feeling sad, "empty, " hopeless, irritable, anxious, guilty; loss of interest or pleasure in everyday activities, loss of appetite—or increase in appetite, sleep disturbances...That's a start.

Many Ways to Tell: Depression can manifest in many ways. Here are the main symptoms to look for in someone: feeling bad about him/herself, losing interest in hobbies/activities, fatigue, poor concentration, poor self-esteem, guilt, pessimism about the future, wanting to die or hurt themselves in some way, sleep problems, eating problems. All aren't necessary, so encourage them to please consult a doctor.