The OP is about a school of Tibetan yoga called g-tummo, but there are many different schools which follow different practices and traditions, leading to different outward attainments. I can’t place exactly what you’re talking about, but those all sound like effects related to slowing down of the metabolism, which is common to most all deep meditative practices.

One interesting yogi to look up is Milarepa, if the less documented but more awe-inspiring stories strike your interest. He seems to have led an incredibly interesting life.