Not sure who this is directed at, but I'm definitely not arguing with you. I've been fighting with it most of my life, too. No, it's not a choice, and a lot of people don't realize that there is a huge difference between "feeling depressed" and "having depression." One is a temporary mood that seems easy to shake off and usually is. One is a genuine medical condition that, unless you've had it yourself, is hard to fully understand.
It's a paralytic. It can hinder every aspect of your life. It can make you feel trapped inside your life, your job, your own body... (not really telling you this, so much as just stating it, since you said you had trouble describing it yourself. This is about the best I can do.)