Classic svt starts and stops in what feels like one beat and is generally from around 180 to 250 or so. Stress and fear can definitely raise a person's heart rate and cause high blood pressure and they can both stay elevated for some time. If you find yourself stressed, try and drink lots of water. This will help take stress off the heart. As well try to do some deep breathing to calm your nerves. Slow your breathing as best you can to avoid producing stress hormones and see if that helps. From what I believe, when it is actually heart related tachycardia there is a specific chemical that the body produces and since your heart tests were normal that says to me that your body didn't produce the chemical and therefore it was likely the high heart rate was caused by outside influences. I know after I had my episodes of svt if they lasted any good length of time I would pee like crazy the next day. This was my body trying to get rid of the excess heart chemicals the doctors were looking for. Since you didn't appear to have any markers in your blood indicating heart issues odds are what you experienced was stress related but good to get checked out regardless. So just try and work on the stress and anxiety. I understand that can be hard when something happens with your child but just do the best you can. That is when your child needs you the most so the more you can manage your fear and anxiety the better you will be able to be objective for her when something happens. Take care.
I'm taking a course on self compassion and it talks about how we treat ourselves when we feel threatened. This is very similar to what happens when fearful things happen in our life like your daughter needing to go to the ER. Our bodies have a primal response system that alerts us to danger. In the past it was necessary to keep us safe from physical harm in an unsafe world. We respond with flight, fight, or freeze. Your daughter was in physical danger and your motherly instinct was to react in a response and run to her rescue. However, this wasn't a situation that you had control over so the response just turns into panic and anxiety and worry. So beyond just trying to slow your breathing down some of the things the course I am taking suggests is that we label what we are physically feeling. This helps disarm it in a way instead of simply trying to push it away which really only serves to cause the emotion to grow stronger. So label and identify exactly what you are feeling. Talk to yourself like you would a friend reminding yourself that things will be OK. And finally hold yourself physically. Hold your hands to your heart, caress your own arm. Soothing touch can do wonders to calm us down. When we are on our own we have to be our own best friend so be kind to yourself when you feel panic coming on and try to respond to yourself like a friend would and hopefully you can get ahead of the panic before it takes over. This stuff takes time. Our brains our creatures of habit so things may not change over night but just try to be more proactive when the panic starts and maybe you can keep ahead of it before your heart rate gets stuck being elevated. Take care.