I appreciate the additional information and commentary, so I'll try to answer as best I can.
Why not? I've already experienced my energy system first-hand with Piti and other sensations. I also like learning and find it interesting.
There's good reason as to why I've said to avoid getting caught up in energetic systems and the models right now. I understand that you like learning about them and find it interesting, so it may be that you're karmically inclined towards these sorts of techniques. However, as I've said it's a deep, deep and complex topic that goes way beyond the characteristics of absorption such as piti.
If you start trying to get involved in manipulating the energetic systems without sufficient understanding of, and experience with emptiness/non-conceptuality and non-duality then you run the risk of seriously fucking yourself up. This isn't scaremongering or superstition; you are quite literally learning how to take control of your nervous system and it's a risky road if you don't have the physical, mental and spiritual capacity to handle it.
I don't say this to be rude or to imply that "oh, you're just not awakened enough" or any of that shit. I'm basing my answers on the questions you've asked, and none of them so far have suggested that you're at a stage where these sorts of practices would be beneficial to you.
If you still want to pursue study of the energy systems, then I highly recommend getting a hold of "Awakening the Sacred Body" by Tenzin Wangyal Rinpoche, and "Yantra Yoga" by Chogyal Namkai Norbu. Those are fantastic resources that we've been blessed with and can provide a more stable grounding for you to work from. The mention of these two great teachers brings me to...
I also disagree that a teacher is necessary. It's ideal, of course, but you can still learn from books/videos/other resources.
You're perfectly entitled to your opinion, but that doesn't negate the facts. Yes, some people can engage with this level of appearances without guidance from a teacher, but that's the exception rather than the rule. You can't 'learn' the energetic systems from books, videos or other non-physical activities, however you can develop a conceptual model that might allow you to better understand what these systems actually
are through direct experience.
As you've said, working with a teacher is ideal and this is because a teacher of Vajrayana has activated and mastered these 'circuits', which means that they can literally point out what the phenomenology of the practice entails. In doing this, many of the pitfalls can be avoided and accidentally shutting down your hormonal system isn't likely to happen...
To double-back to a previous comment:
From my understanding, aligning your energy system is important for overall health, and it also seems like it'd be related to awakening since it's enabling the flow of Kundalini through your body. So I'm a bit confused how this could be a hindrance.
The energetic system is essential, not merely to health but to our very ability to breathe in and out!
Kundalini is a very specific form related to primal drives and imprints. As with the other energetic phenomena, this isn't something you want to start fucking around with or investigating through intellectual curiosity. With respect, you're already confusing yourself by throwing around these pop-spirituality buzzwords without understanding the actuality of what those labels point to.
Premature awakening of Kundalini could quite easily result in major mental health issues, and I mean that seriously. Working directly with these energetic phenomena can and will reveal much about the nature of reality that can and will lead some people into psychosis if inexperienced in degrees of non-conceptuality and non-duality.
There's a very, very,
VERY good reason why spiritual systems, and the supreme Buddhadharma in particular place so much emphasis on morality as the foundation of the Path. I'm not saying any of this to be cryptic, I'm saying it from a sincere wish for you not to harm yourself and for you to truly experience liberation.
How's normal stretching any better? It's proven yoga is beneficial for many things (including stretching), so I don't see why I'd do something different. Plus it's fun and I enjoy it, it's just a part of my exercise routine.
How is an apple different to an orange?
You're using this term "yoga", but you're
thinking about a very specific model and confusing matters for yourself.
What you're
talking about is what we could, for the sake of convenience, call non-Buddhadharma systems like the 8 Limbs of Patanjali, etc.
The practice you're
actually doing isn't the sort of "yoga" that those traditions engage in, and without the appropriate visualizations, mantras and asanas you're not actually doing "yoga" as the word is used in that context.
Without all of the accoutrements, all you're really doing is what I've recommended, i.e. mindful stretching exercises. It's great that you find it fun and that it's helping you to exercise regularly, but don't overcomplicate things for yourself. Continue to do what you're doing if it's helpful to you, but please understand the distinction being made in these replies.
I know it's sufficient to start with, and I'm not even flexible enough yet to even sit cross-legged. I've been meditating on a chair for ages. But it'd be nice to be able to do full lotus sit.
For a beginner, full lotus is not necessary and even the half-lotus can provide sufficient stability.
I've also noticed that when I do cross my legs (although I can't for long), I do feel a bit more energised. And even if it's subtle, it's still worth developing the ability do this because even a small boost in energy is worth the effort if you're doing a tonne of meditation. I intend to do very long sits later on, so developing the flexibility now makes sense so when I get to that stage I can do it more easily.
And it's not just that, I'd prefer to sit on a cushion wherever I choose (such as in nature), and full lotus enables you to do so comfortably.
The increased energy is more likely related to increased bodily awareness that comes with the discomfort. Rather than viewing this as a hindrance, use it to maintain awareness
in the body. Increased energy will arise as long as you remain steadfast and attentive.
People have this idea that meditation is supposed to be comfortable. It's hilarious to me now, because I once thought the same but I now appreciate the power of discomfort in getting us 'out of our heads' and bringing awareness into the body.
This will sound odd, but we need to learn how to suffer properly...
I'm currently following The Mind Illuminated, with the intention to reach stage 10 by the end of the year.
Not familiar with the specifics of TMI, but I believe Culadasa emphasizes anapanasati/mindfulness. Incredibly powerful practice, so go at it with gusto if you find his approach helpful!
My goal is not just to reach awakening, but also to improve my health, master psychic abilities, and other things. So to me, I don't see this as a distraction. If my only goal was awakening, I probably wouldn't bother doing it. From my research, gaining control over your energy system is a key part of gaining conscious control over psychic abilities.
Not being a killjoy or implying that there's no value in mastery of siddhis, but your comments here actually bring pain to my heart. Awakening is
the only goal worth pursuing in this lifetime, and you're already distracted from it by your fanciful ideas about "psychic abilities".
Understand just how fortunate we are to have been born as human beings, with the uniquely good fortune to have heard the Buddhadharma and, most importantly, to actively pursue liberation from habitual rebirth for ourselves and all others.
You are obviously free to forge your own path and I wouldn't dream of trying to force anyone to do anything. What I would
ask though, is that you sit down and reflect on the underlying intentions of seeking mastery of the siddhis, and why you place more importance on this than seeking awakening.
Practice well, my friend.