It sounds like what happened is that you had an aggressive episode. And if this was your first one, then I’m sure it was quite disorienting. Aggressive episodes can be hard to predict and can come on very quickly (or can seem like they came on quickly even if your anxiety has actually been slowly growing without you noticing it). One way or another, your dog nipping you seems to have set off a cascade of emotions that overwhelmed you.
This is a thing that happens. You’re not insane, and you’re not an awful person. You did do something harmful, however, and so it is important to learn how to recognize that you are about to have an aggressive episode and how to control it. This is not easy, but it can be done. As you noticed, there was a point at which you felt like you lost all control over your body. And in fact, that’s exactly what happened: you lost control.
The good news is that you can redirect your anxiety and your anger before you lose control. The point of no return, after which you cannot stop yourself from losing control, is difficult to identify. It requires you to really pay attention to the way an oncoming episode feels. But if you can learn to anticipate it, you can stop an outburst before it starts. You won’t get the release of the aggressive episode, but you also won’t have to deal with the shame of the aftermath.
Ideally, you will learn to recognize an oncoming episode well in advance. You can then do something to relax before you are even close to losing control. If you don’t already know how to release your anxiety, a therapist can help you figure out what sort of calming techniques might work for you. Some people work out their anger by punching pillows or hitting trees with sticks. Others eliminate it through breathing or meditation. All you need is something that works.
Unfortunately, there will also be times when an episode comes on quite suddenly. To deal with those cases, you have to learn how to control it in the moment. What you are looking for is that point at which your brain just gives up and lets the anger take over. There is a way you will feel just before it happens, and that’s your last chance to prevent an outburst. It won’t be immediately obvious what the feeling is and when it happens, but you can learn to recognize it over time.
This means that you might have to go through a few episodes before you learn to control them. But this is another area where a therapist might be able to help. A therapist can go over your recollection of the incident with you in person and look for specific clues about when you pass the point of no return. They probably won’t be able to solve the problem immediately, but they might be able to significantly shorten the amount of time it takes for you to regain control.
It will never be easy, and it will never go away completely. But it gets better over time, and you can learn control.