You described a lot of the symptoms I experience during a depressive episode.

Honestly, I question whether anyone can have a "miserable" personality without qualifying for a diagnosis of a mood disorder. As being miserable can really... drive one mad.

People will call you miserable. People know about my diagnosis and STILL call me a miserable person, or act as though I stare into space for hours to spite them or something. Those people, I find, aren't often worth the effort. You cannot explain depression to someone who doesn't understand.

Part of depression (and many psychological conditions) is denial. It's common to wonder if the depression is just in your head, or if you're exaggerating it and your behavior is just 'normal' for you.

You just described depression. You're not overreacting.