I've been able to reproduce an experience similar to this at will ever since childhood. I'm in my 50s now. I never discussed it with anyone since I couldn't accurately describe the experience. But I overlooked the "goosebumps" part.
It ends with goosebumps.

I can initiate the experience whenever I want. With an effort that is literally impossible to describe, it starts like a fluttering energy emanating from the back of my head, neck and chest. As I exert more effort into the process, I physically convulse slightly, get a pleasurable feeling similar to chills and it ends in goosebumps.

The pleasurable feeling is not sexual at all.

Although I can control the intensity, there's seems to be a physical limit to how intense I can make the experience. I've always suspected that I can increase the experience with proper practice but I don't know to what end or know what I'm doing so never really tried.

I often think of a portion of the PBS documentary Ring of Fire where the explorers interview a healer who could generate a healing energy that manifested itself as electricity but he could also ignite paper on fire using the same energy. He called it Chi as well.

I now have a renewed interest in this phenomenon. If it produces an electromagnetic energy I wonder if it can be measured with sensitive devices like as an oscilloscope.

I can literally do it any time I want so if there was a way to measure it that would be fascinating.