Good morning, I didn’t realize you posted this twice and left an answer for you in the other comment.
Here’s a cut and paste of my reply for you. I hope you’re feeling better this morning. ☺️

Since you’ve discussed this with your doctor and didn’t find any underlying medical condition, this sounds like the classic symptoms of a panic attack. They’re horrible and it seems when you have one, the thought of possibly having more fuels the anxiety level, doesn’t it? I suffered from them too, about 40 years ago. I hated going to bed at night for fear of waking up with the symptoms. You’re right, it is a feeling of dread and doom!

I was able to get control of this through bio-feedback, which was a “newish” technique back then. Now it’s mainstream along with other mindfulness programs to help you get anxiety and the panic attacks under control.

Mindfulness therapy works. If I would feel an attack coming on, with the tools I learned on calming myself, I was able to ward off the attack. It’s a matter of realizing “I’ve been through this before and I didn’t die.” I learned that I have the ability to override my emotions and calm my mind and body down.

I’ve found several good articles for you this morning to help you understand you’re not alone in this. These articles discuss the symptoms and potential causes of panic attacks. The last article has some calming meditation techniques for calming.
https://www.midtownnephrology.com/panic-attack-symptoms-and-treatment/
https://www.mayoclinic.org/diseases-conditions/panic-attacks/symptoms-causes/syc-20376021
https://www.verywellmind.com/symptoms-of-a-panic-attack-5207966
https://www.verywellhealth.com/how-to-stop-a-panic-attack-5202930
https://www.verywellmind.com/mindfulness-meditation-for-panic-disorder-2584082
Let me know what you think!