How can I know if my moods are normal or depression?

Degree, not kind. People can be sad about events or losses in their lives, and normally go through periods of discomfort or unrest. They can grieve when someone dies, for instance. But if their temporary sadness deepens & extends, and there's complete loss of interest or pleasure plus changes in sleep, energy, & appetite, their condition may be depression. Especially with suicidal thoughts, get help now.