This has been happening since I started high school last year, I've been talking/singing to myself and having full conversations with no one else but me (or my dog/fish/cats/birds) and then sometimes I just burst out laughing and don't even know why!
Others I start going into hysterics because of something that happened 5-6 years ago, or because I pull faces at strange moments.
I haven't really thought about it until today, after I burnt my finger, I started talking to myself in Scottish saying stuff like;
"Ach! I've burnt ma finger after making stir fry! After? Not during? Nah, after! Through the cloth! It was supposed to protect me but i was burnt! My dog is a wittiness! arent ya? Aye! She burnt her finger! i saw it with my own eyes!"
When I got upstairs I suddenly became conscious that I do it quite a lot.
Not when I'm with friends, it's mostly when I'm by myself or at work, I sometimes argue with myself in my head, I've said some things out loud in front of my friends and they don't have a clue what I'm talking about.

Am I insane or is it just something normal people do as well (being eccentric)?:confused:

Sounds like your just eccentric. I sing and dance to music in my house in a way I would NEVER do in public.

I say weird things all the time too, and to my knowledge, I'm sain!

Haha, and I do the scotish thing too, sometimes Irish. For example, if I have Lucky Charms for breakfast, I run downstairs and yell, "AYE! WHERE ME LUCKY CHARMS!?!" when I am alone, and no one can hear me.

I think you're fine, and don't worry. You're just happy! Of course I don't know you personally, but you seem fine to me, in my humble opinion.

I went through some form of depression a few months ago, where I planned out how and where I'll set myself up to be murdered by my friend, but I've changed dramatically, like you said I'm happy, but I don't understand why.

All that matters is that you're happy!
If you fall back into depression, maybe there is a problem. Is there a reason you went through depression? It could help to know why you went through the depression, so it doesn't happen again. But, if you're happy now, just stay happy!

If you realize you are doing it and are able to even worry about it, you aren't mentally ill.

I don't think there was a reason I went through it, I just wanted it to happen, I wanted to hear people screaming and feel what it was like to bleed to death after being shot by a friend (kinda creepy when I think about it) Sometimes I get the odd moment, or day where I think about being murdered on the bus home from school, its gruesome, but then I remember where I am and turn that thought into something funny.
I just wanted to make sure I wasn't ignoring something important, I only realized it an hour ago when I was laughing.

Yeah, you know what? You're just happy. Don't worry, you're not mentally ill. You actually seem more mentally fit than most people. Just be happy that you're happy!

LOL... you are young and creative and just trying out a bunch of stuff. Maybe, you'll be a funny lady when you grow up?

Best wishes, :)