>>2 I think it's a little different than that.
Everyone feels bad sometimes, some more than others, but everyone does at some point in their life. People want other people to care about them and they want them to understand what they are feeling. If you tell someone you are sad, they say that sucks, etc. But, if you tell them you have depression, they are suddenly more interested.
I find people tend to use mental disorders as a way to convey the feelings they are having. Incorrect self-diagnosis are almost always based on some truth, so if you talk to yourself, you may think you have multiple personality. It's also a way to solidify your experiences into some official 'thing' that everyone can understand. Instead of just feeling sad, which can be interpreted many different ways and doesn't fully describe what you are feeling, having depression means you are actually going through something. It's a way of making your feelings into something you have overcome, or more generally, something that is universally recognized as a difficult experience.
Unfortunately, there is already a thread for this.
http://dollars-bbs.org/personal/res/1382215490.html