I made an account to comment on this. I experience a similar thing but the generation feels like it comes from the base of my spine and travels up rather than down. I've been rather unsuccessful at finding out anything substantive about it. There's a lot of woo surrounding it - I'd recommend checking out what people say about Kundalini meditation as it seems to describe what you and I have experienced.

When I was a child I thought it was conscious generation of adrenaline. Now I'm wiser I know that's probably not true, but it certainly feels very similar.