Did you know it's not uncommon for people experiencing a panic attack for the first time to go to the emergency room thinking they are having a heart attack? We're definitely not alone in our experiences.
I've experienced similar issues like nausea, lack of appetite, upset stomach, dizziness, lightheaded-ness, racing heart, arrhythmia, chest pains, stiff neck, stiff everything, soreness, and numbness & tingling in my hands, feet, arms, and legs.
I don't know if it's comforting for you, but I personally feel some relief knowing that there's nothing wrong with my heart or nervous system--it's "just" anxiety. It's astonishing how and how much anxiety can affect your body!
It's also frustrating, because I often feel weak for "letting" my emotions wreak such havoc on my life. But I know it's not about "just" and "letting". There's no "just" about anxiety and it's not as simple as "letting" myself get worked up. If it were that easy, no one would have issues in the first place.
I've had trouble with anxiety off and on for most of my life. I've been better than today -- I've gone years without even thinking about anxiety. There are lots of things that can and will help, but it's different for everyone.
One common characteristic of anxiety is 'loops'. Thought loops and feedback loops. I feel bad. Because I have anxiety. Feeling bad makes me anxious, which makes me feel worse. Et cetera. It's easy to get caught in those loops. For me, it's important to identify and understand them so that I can stop feeding into them. Breaking loops and helping my body manage "the freak out chemicals" better are helpful. Taking a walk sometimes serves both purposes.
Another common characteristic is avoidance. Consciously or not, I tend to avoid anything that makes me uncomfortable or requires a lot of effort. Having an anxiety disorder means I'm tired and feel bad a lot of the time, so I don't feel I have the energy. Unfortunately, many things that help manage anxiety are hard to do, really hard. Feeling bad makes them even harder to do. But if I were to do them, I'd feel better.
Anyway, you might find formal relaxation exercises are more helpful than trying to relax casually. A while back I used to practice meditation, which as a side effect, taught me a variety of breath control and relaxation techniques. At the time, I was doing it it was because I was into New-Agey stuff. It was only later, when I'd fallen out of the habit for a few years, that I realized that it had been a major factor in helping me manage my anxiety and I learned that CBT involves relaxation exercises.
I'd post some links to examples, but I don't have the required post count. Try googling for CBT relaxation exercises.
I have a tendency to isolate myself when I have anxiety trouble. It's something that I need to do, to some extent, but it's also unhealthy. It lowers my stimulation, which is good because I'm overstimulated and oversensitive to stimulation. But it also lowers my threshold for stimulation over time. Try not to let yourself get too isolated--it can end up depressing you.