What are the differences between actual depression and severe mood swings in a preteen child?

Thats a dificult question.
I have been a moody teen. Hated my parents for no reason, always walked a few steps behind them. And felt like they were trying supress me. Silly really.
I have also suffered depression.
Depression was debilitating. Instead of being ‘pissed off’ at the world and laying in bed till noon due to lack of motivation. I layed in bed as I was suffering a debilitating mental colapse. I wanted to die. I felt as if I was dying. Instead of melodramatic thoughts of death.
I think it is a fine line for anyone on the outside to be sure what is going on inside anothers head. I think professional assessment would be required.
Better to book an appointment and have an annoyed child than shockingly have a suicide attempt and realise that you did nothing.