I was depressed for the longest time - honestly felt like an eternity. It's still ongoing and has been for I'd say more than three to four years(?), thankfully though, I'm much better right now and more loud and very funny, according to my mother, although I still get into very frequent slumps where everything just seems hopeless. It was after my parents' divorce, and my dad was the one to move out. I saw my mother as the one behind it all so basically I took out all of my anger and hatred on her. I was very irritable and developed a very negative outlook on life. It started off as a general dislike to everyone, noticing all of the bad things about them and then not wanting to be around anyone 'cause they would annoy me. Things escalated quickly about last year when my mom and I got into a huge argument, which honestly messed up our relationship - we're still trying to fix it-, and afterwards I tried to commit suicide, even made numerous suicide letters to my mom blaming her for it all. But it was as I cried on my bed, nauseous and sobbing, that I really reflected on my life. Personally, I feel the thing that helped me with my depression was time. Yes, when I moved schools and met my only friend I felt less lonely, however, lots of time thinking about who I wanted to be and what I wanted to do in the future helped me think about my mistakes and put them past me.

To be honest, I've never been diagnosed by a professional before, nor have I met someone who has been diagnosed with depression from a professional. However I've read a lot of stuff about it and there's a lot of symptoms.
Depression is not just a one time thing. If you feel sad after you experienced something tragic, that's not depression. It's just a normal kind of sadness. However, depression is different. It's always there. No matter how much you want it to leave. You might not feel sad 24/7 but you will always feel tired, worthless, untreatable, alone. And you'd know you have depression once you start having suicidal thoughts. Again, depression might not be obvious to other people as most of the time it hides in one's thoughts. One might not act out their suicidal thoughts, but the thought itself is strong enough to kill.
Hope that helps!

If you get depressed for 4 hours and then become alright.
It's probably a minor depression episode.
Happens with people most of the time.
All of us feel low but we still keep going on.
Just relax.

Depression is sorta like that.
Sometimes it's hard to explain why you get depressed, you just feel so lost .
Just feel like giving up on everything you ever worked.
Shutting yourself from the rest of the world.
Not making eye contact with anyone hoping they don't stop and talk to you.
You just feel like being alone and cry and cry and cry .
That's depression for me.