HELP, PLEASE? (It's very long, but please read!)

About a week ago, me and my dad got really into the biggest fight we ever have had (although we get in quite a few, this one was huge), and I was just sooo mad to the point of breaking the windows or something, and I knew I couldn't do anything to him, so I just looked down and kicked my dog. It was almost like I "anger blacked-out" (if that makes any sense). I looked down, and yes I saw the dog, but I was just sooo angry I had to do something, and without fully thinking over how it may really hurt him, I kicked him... hard. I felt sooo guilty and still do, because he started kind of limping (it's getting better now, I think i just may have bruised him), but I've just felt like complete scum of the earth for it. I've tried my best to help him out by helping him get on the couch and such, but I just can't forgive myself. I love animals and would never typically hurt any of them!
Anyway, a few nights ago I was watching Investigation Discovery, and it was an episode about women who violently killed their children, and it got me so worried; if I can hurt a poor innocent dog like that, what if I turn out like one of those women when it comes to my children when I get older? I started thinking, what if I killed someone/something; would I even feel guilt? What if I didn't? And why was I even having thoughts like this? Am I going crazy? And I started thinking things like, "Why do we even like animals?" and "How much does a life really matter?" Of course deep in myself I know I love animals, I always have, but I just don't know. And I started thinking, "What if I'm a cruel, terrible, future killer?" And I keep thinking, "Would i really care if I killed an animal, or ever somebody?" And other thoughts like that. I've been worrying myself to death for almost 3 straight days. It's constantly on my mind, and I keep wondering why I had these thoughts in the first place? I've lost my appetite, I keep have stomach/digestion problems, I feel so uneasy and trembly inside, I don't feel like doing anything, nothing can't seem to make me happy, I keep fiddling with things in my hands, I can hardly sleep, I'm really dizzy and light-headed, I can't seem to get enough sleep even though I can barely go to sleep, I've been feeling like I'm dreaming/in a daze, etc. I've even been watching animal videos on YouTube hoping to convince myself I do, in fact, love animals. And I keep thinking, "Did I really feel guilt for kicking my dog, or am I faking it?" I just obsess over being a good person, and I'm just afraid I'm really evil and cruel, pretending to be nice and caring.

ALSO something that may be important to know, I was diagnosed with anxiety 6 years ago and had a lot of panic attacks (usually over feeling sick, though), and have been taking Sertraline (generic Zoloft) (50mg) ever since, and have done lots better. I also have a lot of time on my hands and sit around and over-think E V E R Y T H I N G. I mean EVERYTHING. I've felt this same uneasy, shaky, scared feeling back then as I do know, but never over anything like this. I've never had thoughts like this before, and I just don't know what to do.

I researched a lot, and I came across "intrusive thoughts" and Obsessive Compulsive Disorder. It seemed to fit my situation a bit, but what if I really WOULDN'T care if I killed/hurt someone/something? What if I would feel emotionless about it (because I'm afraid I would). I feel like my true emotions have been turned off for days, and fake ones on, if that makes any sense at all. Safe to say, I've decided to not watch anymore Investigation Discovery (although I have watched it a lot, and it's never bothered me before, I don't understand). I've thought that maybe I just felt so guilty about doing that to my dog, that I thought I was no better than those murderers killing their children on that show, that I was afraid I was no better than them, and I would end up doing so, too. I'm afraid that secretly in my heart I have killing "wants" though, and I'm just a shaky, crying mess, I don't want to be that type of person.

Things to know:
- I just started taking Metformin and a thyroid medicine (I'm not 100% what it is called, and can't go look right now) about 3 months ago, but could that really mess up anything?
- I'm a female.
- I'm 16 (turning 17 in a few months).

I'm sorry to write so much, and it's probably very confusing, but I just really need some help/advice/reassurance. I feel like I'm really going mentally ill, and I'm terrified out of my wits. Please, please answer seriously. I really need some advice. I thought of therapy, but:
1.) I'm nervous about physically telling everything to a stranger.
2.) I don't come from the richest family.

But please, please give your advice/thoughts. Thank you so so so so so so so so so so much, ahead of time. xoxo

Hi, I'm not sure what I can say to help but if you're thinking about all that, you're probably not evil. Cause I don't think an evil person would question whether or not they're evil. They would probably be like: "Oh, I'm evil. Cool." But you're not like that. Therefore, you're not evil! If you're not comfortable with talking to a stranger, why not a trusted friend or relative, preferably one that knows about your diagnosis. Also, you feel guilty about kicking your dog and even tried to make it up to him. That's not very evil, is it? Anyway, maybe if you prefer trying to solve this without telling anyone in you life, maybe beat the thoughts with logic. If you're comfortable, watch movies/shows about evil people and note how you differ from them. Hope this helps <3<3

You said it yourself. I do not think you should doubt if it was insincere. This in itself means that you would not be guiltless if you hurt another being. You are not going crazy. You did something bad, you can now learn from it. Now you know that when you allow yourself to get that mad, you can do harmful things. Don't do it again. If you can not consciously make the decision to not harm another being or thing while that angry then do not allow yourself to get that angry. Walk away before you get there. You are fortunate to have learned something about yourself and be able to learn from it. Take advantage of that.

Might be worth seeing someone about this, before it turns into something that really messes with your mind; by this, I don't mean "before you turn into a whack-job", but rather, but this screws with your mind like it has/does with me. I did something similar, when I was a kid, on a somewhat worse scale, and I've gone through many years of guilt.