Crosspost from KFD, just wanted to get some opinions here!

40 minutes sit. Started with mindfulness of breathing, staying with the cohensive flow. Concentration flowed easily. Points of itching came up but I disregarded them and kept with the flow of the breath. After 10 minutes, shifted to sensate fragments of the breath. Breath was "chunky" and full of disctinct pulse-fragments. Noticed a heartbeat-like pulse start to form in the crown of my head. Followed this pulse which spread to my whole face. Felt like my whole face was pumping blood. Eyes started to get a little twitchy. Focused on the twitches and all of a sudden my eyes basically rolled back in my head and shit started to get crazy. My eyes were twitching uncontrollably, I was breathing extremely fast in and out of my nose, my heart started to pound. All of this was completely involuntary and really wild. Thoughts of fear came up as well as a desire to just open my eyes and stop but it just kept going on its own. Was able to relax a bit and just be with the violent twitching/breathing/pounding. Eventually this started to slow down and subside on its own.

Body felt completely energized, especially in the hands which were very tingly. The breath was completely smooth and refined and I could barely note any fragments at all in it, it just felt totally cohensive, even when I tried to bust it to pieces. It became slightly difficult to concentrate. Kept following the breath and just letting go of any effort. Eyes started to twitch a little bit again, and then involuntarily started to shut harder and harder until they were squeezed shut. Felt like I was inside of a spacious void. Observed the grainy-ness of the blackness. Eventually eyes eased up and weren't tightly shut anymore.Kept following the breath. Was aware of the pulse in my eyes, only this time the peak of each pulse was made of up very distinct mini-pulses/vibrations. Kept following this pulse for the remainder of the sit.

Right now I feel energized and shaky. My teeth are chattering but I'm not cold.

So: what was that?

Hey Bud,

Welcome to the DhO.

Going by your descriptions, I'm assuming that you have some knowledge of the standard maps of insight practice commonly discussed on here; I'll suggest that you have just crossed the 4th ñana, Knowledge of the Arising & Passing Away, as your descriptions sound typical of this stage. If this is the case then it indicates that you are practicing well enough to be making progress and so, assuming that you haven't yet attained stream entry, you're on the right track towards enlightenment.

If you haven't already done so, I highly recommend checking out Daniel Ingram, the founder of this site, and his book "Mastering the Core Teachings of the Buddha" which is an excellent starting point for anyone looking to learn about pragmatic/hardcore dharma and get results in their practice. In particular, I would suggest reading this chapter and seeing if any of it sounds familiar to you.

Either way, don't panic or think that you're dying or anything silly like that, this is just a natural part of the process but the stage you've just experienced is a turning point for anyone interested in 'getting' enlightened so it, and the potentially difficult, but not inevitably so, stages which follow it.

Why not start a practice thread to keep track of how you're getting on, it's a good way of learning and you can get some excellent advice from people who've walked this way before.