You've described the two main types of Depression.
Reactive Depression, and Clinical Depression.
If your much loved Pet died, you would be Depressed, maybe for weeks to months.
That's Reactive Depression
But if you had everything going for you in Life, like Love, Money, Houses, Cars, Holidays etc, but you wanted to Commit Suicide, well that's Clinical Depression.
Recognising that you have Depression is the first step.
But doing something about it is the second step.
It's hard sometimes, to realise that you have a problem that needs fixing.