Intense Zen training with great friends, Sogaku and Shinjo.
Lately I’ve been doing a lot of  Zhan Zhuang, and as I do it, memories of energetic insights, of struggles and specific leaps in practice have been coming back to me from my first couple of years in Zen training.  I think describing some of that feeling will be of value to some training people out there going through difficult training, and feeling lost or isolated in this process.  As a person who has been through much of this, it all seems normal, and once you have walked it, you can help others through it.  All that I describe in this post is not an idea, but a continual, cultivated felt sense. As Zen training is not so much a strict religion as a yogic transformation process, describing some of these energetic activities might be helpful for some training people.
There is a particular type of zen student.  They have a burning temperament, a kind of desperation, a fascination. Perhaps that person has certain energetic problems that have brought them to practice.  This all can give that person a kind of one-sighted concentration. Usually they do the energetic work because it feels like their only choice in life.  They are often looking for the most intense training environment available.  An environment to push and to be pushed by.
For this type of training person, their experience of life is at a high volume, and not always in a pleasant way.  An intense Zen training environment raises that volume, and it becomes all encompassing and inescapable. These Shugyoshas (people of intense training) are learning to ride this energy, to wield it, to tame it, to settle it. It is a burning hot process.  It is life on the line.  Pushing ourselves beyond our limits. For some, like me, doing that training was the greatest relief.
Let me first say that all that I am writing about here should be in the context of a student-teacher relationship in a contained environment.  A good teacher will know and be able to handle anything that you throw at them.  That is their gift to you.   Also, Zen is not for everyone.  If a person is psychologically unstable, it might be a better fit to work with another style of practice.  Check with a doctor if you have concerns.  With that said, here are some words of encouragement:
I recommend that you do your energy work every day, do the body practices that help bring that energetic process to life. For me that was Zhan Zhuang, Qigong, Non-directed body movement, but others might work for you. If you have a volatile energetic orientation to practice, then you’ll need these practices to sort yourself out, to bring yourself into oneness.  These practices will give your internal world a sensory language to interact with this energy, and have it begin to work for you and not against you.  I can say that I was a walking ki problem for years before I immersed myself in Zhan Zhuang and Non-directed body movement to support my zazen.  Through these body practices, this energy will begin to align, come into oneness, begin to unify in one direction, rather than in subconscious chaos.  With experience, it will be clear where you are stuck, and your internal sensations will learn how to release these stuck places.
Constantly use creativity (kufu), twenty-four hours a day to engage with this energy. Continually find a way to face it, nurturing it in daily life in every waking moment and in zazen on the cushion. Engaging with this process will become more who you are than something you are doing sometimes when you remember.  Do it until something is always unmistakably moving through you, and has its own momentum.  This will take time.
This energy will have a life if its own. Continue working to creatively express this process through your body and awareness.  I’m talking about a process of opening up to this energy, allowing it to flourish.  Letting go of control of it.  Letting the horses run free. We are unconsciously holding ourselves tight to strangle this great life energy moving through us.  Keep opening up to it, even though you have fear, doubt, feel out of control, or feel like the energy is turning you inside out. Have the courage to let go into it, it will take over your focus.  It will become the main content of your experience.  Let go, and Grasp it with all of your being, all of your focus (shikkari)!
This process will feel wonderful at times, relieving to open up energetically, but also your body will struggle to handle it, like shells cracking, opening this cage, over and over.  Scary.  Uncomfortable.  Nauseating.  Yes, but keep going. Deeper and deeper.  More and more transparent.  This process is done along with the Tanden work.  It is a part of this huge process, for many, it is part of opening up the tanden, but as the tanden energy strengthens, you’ll be rooted as well as full and taut.  The experiential knowledge gained through this process will translate to everything in life as we phase through your entanglements into a new wide open vista of reality.
Gradually you’ll be less afraid, as you trust it more and more. Don’t close down to this process.  Be wide open to it, opening up all of your senses, like a great mountain.  Be brave, curious, honest. Trust it. The ancients went through the same process.  The universe is on your side.  Do not shy away from it.  Do not become small.  Use all of your intensity (Not force!) and put it all into this energetic work.  This is the time to put all of your intensity into something.  It really is like swallowing the entire ocean.
Further and further. Allow this process to obliterate you. Believe it can happen. Fall in love with the process, feel it transforming you. Let go of the calculating mind. And as it deepens, you’ll feel yourself buoyant in a new way, as if you are supported from something boundless.  Again, let go into this process.
Release wherever you are stuck, anywhere you feel tense.  Even if it makes no sense to you.  Even if it feels like you are exploding.  Even if you are not standing or sitting right.  Even if your posture gets goofy at times.  Gradually your body will work on auto-pilot to sort this energy out.  Have faith in this process!
Deeper states of mind will happen as a matter of course.  Often people think getting into samadhi is difficult.  But conversely, they think being in samadhi is easy, and it can be, but it also can be a razor sharp process.  Give it all you’ve got!  Slowly ripen from there.  It is such a sublime process. Please keep going.
Go straight. Walk it honestly.  Make a choice to realize it at all costs. Be still in this internal alchemy process, don’t look away. Keep going even if you can’t see anything around you, even if you don’t know what is up or down. You may feel like a wild animal about to explode.*  You may feel like an electric cord forced to be a conduit for more and more electricity. Or feel completely transparent, completely vulnerable, naked.  You may find yourself alone in a space you cannot fathom, but you’ll have a connection to this light there to guide you.  More and more open, more and more transparent.  Keep going until one day this process fundamentally resolves, and then your life will be permanently transformed.  Give yourself to it.  Don’t force it, but put it all out there!
You heroes and heroines embarking on this most important life mission. You can do it!  Walk it that honestly! Realize your true nature!  You who are reading this, and know and feel what I am describing, (you live wires!) or have had some hints of it, thank you!  I’m writing as a fellow training brother.  I’m sorry I can’t be there more for you. But I hope these words hit the mark.  Keep going.  Comments and questions welcome.  Please share this post with anyone who might benefit from reading it.

*Again, just reiterating that this process and intense practice should all be undertaken under the guidance of a legitimate teacher.