Reading this thread, I can associate with what a few people are saying. I've never been to see anyone, but I've had periods where I've definitely been in troughs.
I dropped out of uni after two years for no reason that I can fathom other than I couldn't do it anymore. I tell people I failed a unit, even though that's a lie. It's just easier than the follow up questions. My girlfriend at the time said she thought I was depressed, and had the NHS website up, and I identified with a lot of the markers. Couldn't bring myself to think I was though.
I was a lot worse a few years ago though, when the same girlfriend (over 7 years from the age of 15) broke up with me. Then I lost my job, and my flat. Ended up drinking every night, doing drugs etc. but of course I was still fine.
I thought about ending it, and had an idea in mind. My parents though made me move back in with them. My mum works with people with mental health problems, and I think recognised the state I was getting into. My parents really helped. It took a while, and I still won't admit it to anyone, but I genuinely think they saved me. I've never talked about this to anyone before, and I like the anonymity of the Internet.
I'm living on my own again now, have a reasonable job and a new girlfriend, but I still struggle from time to time. Starting to feel it a little now, hence why I've decided to actually talk, even if it is to p and b!