I don't consider feeling sad about something bad that happened depression. That is a normal response to something. To me depression is feeling bad when I don't really have a reason to. Or feeling too bad about something that happened. Too bad for too long.
What causes that? Why do I react differently than other people?
The direct cause of depression seems to be mainly a decrease in serotonin levels in our nerve synapses in our brains. Norepinephrine and dopamine are two other neurotransmitters that have been implicated as well
Why do some of us have this problem and not others? Partly genetics, partly who knows...Researchers have also found that chronic, low-grade inflammation in our brains worsens depression and Bipolar Disorder and Schizophrenia. Does it cause it? Probably not. I have 2 sisters and I am the only one who got Bipolar Disorder, and we were brought up on the same diet. I started going weird at age 14, and they were fine. Totally unfair - why me?!
But, you know, I think we're stronger than other 'normal' people. The depression, the despair, the mental anguish we struggle through every day of our lives would probably bring them to their knees in a matter of hours. I'm 50 now, which means that I have been depressed for almost 3/4 of my life (72% of it, actually). I'm Bipolar but I started with depression and spent my twenties curled up in the fetal position crying after work, spent my thirties wishing I was dead every moment of every day, was hypomanic then manic interspersed with depression through my early 40's, and then ended up with rapid cycling Bipolar I in my late 40's. Plus Post Traumatic Stress Disorder from having my pharmacy firebombed just before its 4 month anniversary and then a year later being robbed at gunpoint there by drug dealers. Until then (2011), I was successful. But bad things happened and now I feel incredibly mentally ill. I lost my house, my life-savings, everything - and had to start all over from nothing at age 47. I've turned out stronger than I thought I would ever be.
So be proud of yourself that you've made it this far, and know that you aren't alone. There are a lot of us out there. And we're here on this site to talk to each other and give support - because we've been there, done that, and we know exactly how you're feeling.
For me depression is seeing the dishes need to be done but you can't get the energy to do them. Thinking about past events to much asking why, crying for no reason, getting mad for no reason. Hearing a song and start bawling, just feeling low and not knowing why.
My doctor explained that depression is a medical problem caused when brain chemicals are not in the correct balance, resulting in depression symptoms. Anti-depressant medication can help maintain a better balance. According to research, talk therapy along with medication has the best treatment results.
To me, depression is that feeling that everything is vague and doesn't really matter. Good honest grief or sadness as a response to an event or loss is healthy and natural. This feeling of "it doesn't really matter anyway" to me is depression, living in a gray fog, like the world is in varying shades of non-color.