Epicenter... First, thanks for reporting the discomfort!

And yes, Valentine's suggestion about stopping the Key Sound practice for now is right on!

How old are you?

What is your health and medical history?

Solar plexus is an energy center to be sure, but that's also in the neighborhood of your heart! Not just your emotional heart, but your physical heart!

When's the last time you had a physical? Do you have any history of heart-related issues, physically?

Any history of (physical) heart-related issues in your family?

A burning sensation sounds rather intense.

I would say suspend any further practice of the Key Sound Protocol until you've had a medical evaluation and clearance that your cardiovascular system is ok.

This is non-trivial... This practice leads to moving a LOT of energy through your physical system, and your body is definitely telling you that something is asking for attention.

Do a thorough pre-flight check with an MD before taking off!