1. How do you know for sure that you are? Do you just know? Not really. You'll be into it a long time before you realize and even then there's a good chance you won't believe it even if other people tell you. But when you do understand and accept it, it makes a lot of things make sense.
2. What were the signs that told you you may be depressed? My social life deteriorated to nothing, I got into a very repetitive schedule day after day getting nothing accomplished. I never really said to myself "I must be depressed" and if I did was too young to understand what that truly meant anyways. I just wasn't happy.
3. Did you ever doubt that you were and that it was just all in your head? Yeah. It makes it even harder. But the thing is that when you are depressed, unless it's situational, it IS all in your head. It's a negative bias on everything so even if good things happen you'll filter out all of that and be left with the bad.
4. Does something have to set you off so that you go into a depression? In example, a loved on dying. Or can it just sneak up on you and come over you for no big apparent reason? Both? It's very complex and varies from person to person. You can have a chemical imbalance, you can have something tragic happen and as a result spiral into a lifestyle that leads to depression. Generally in my opinion it won't be the loved one dying or the lover leaving, it'll be what you do after that will depict whether or not you become depressed. But at the same time I'm sure there are cases of people being hit so hard by something unforeseen that depression is the result. That's the thing about depression, there is no manual to say what is and isn't or what caused or didn't. It's a very gray area and it's incredibly difficult to document because it's, for the most part, psychological
Sorry if these questions are personal. I just need some answers ...