I don't think I've got a mental illness, I've suffered depression here and there, but never to a massive extent, it never affected me in a profound way like I've seen it do to others. If you knew me in real life you'd likely think I'm a well adjusted 'normal' bloke that's just a bit grumpy sometimes, if there is such a thing as normal anyway. I met a girl on a date once, years and years ago and despite me being all happy and in impress mode she said I had a sadness in my eyes, I guess that's a good explanation - even when I'm fine to the outside world, inside there's something wrong and always has been.
I've just had so many knocks, each one gradually worse so that I've just had enough now. I've had suicidal tendencies for a long time, even when I was relatively content and had a lot going for me, and even then I wondered why I couldn't be happy when I should be happy, like is everyone like it and hiding it the way I'd been doing or do some people genuinely feel happy? It'll sound glib but I just find life a real chore, it bores me, I don't like most people, I've never felt like I belong in this world. If that makes any sense to anyone.
I'm sure a psychologist would love to give me a label though, they'd feel they'd failed if they couldn't spot some tendency in me. Most likely bipolar as I have days when I'm an arse to be around, and some when I'm a lovey dovey hearts and Unicorns person.