I always had shakings... they are my own meditative pain in the ass (I think everyone has their own...).
I'll try to share something of what I've learned about them, hoping it's going to be useful.
From an insight point of view, they are not that bad as they look; that's what I did: I appreciated how they was going by their own, and after a while I kind of relaxed into them: my body was shaking, and I felt still, not doing anything in particoular, just allowing them to do their thing. In the beginning you will feel a resistence, but in the end you will become comfortable with them. They are very very easy objects of insight, they can easily get you to stream entry. You dont' need to pay attention to them, their sensations and their uncontrollability are completely obvious. Basically, you practice the
Mahasati meditation tecnique, using them as an object.
Practically speaking, what you do is just to put the center of you attention on a neutral, non-shaking spot, like your chest, and then you just wait, allowing everything that is going on in the background to show itself.
Also, and this is an important point, there is for sure a part of you that is fueling them; I strongly raccomend to spend some time observing the intentional component that make them continue after they begun, and becoming more and more able to stop them not at will, but just letting go of that intention.
I'll try to rephrase: basically, it's not very clear if they are or not volountary: on one extreme there is the feeling that they go completely by their own, like everything else, on the other there is the feeling that it's you who decide to shake, but you can't help but deciding to do that. The more you pay attention to how it feels that it's you doing it, the more you can stop doing that at will. As you see it's something that you do intentionally, you also see that you can stop doing it, exactly as you would stop doing anything else.
If you don't do this, this thing can very easily take a life of it's own, expecially if you are using them as an insight object.
Wich means: watch them, see how they are uncontrollable, but also try not to fuel them unnecessarily.
If you want to make them go away, I wasn't able to do that, not yet; however, that's the pointer I'm following: you might find that there are sensations of tension arising before they begin; if you can catch the sensation (that tension can be very painful), you'll see that you can just make intentionally that tension flow in your body, and it will not cause you to shake any longer; also, the more the sensation can flow, the less it hurts. However, this process can be incredibly painful, so I'm not sure I racommend this. Also, you might find that, eventually, that sensation just trasmutate at some point during the flowing in some kind of emotion. There is kind of the risk to open a pandora's box here... you've been warned!
If you want to practice concentration, the best way to go I know of is to observe the breath, and getting really into it, feeling how "you" are going up and down with it, completely ignoring the individual sensations and just allowing the breath to cradle you. In my experience if I can do that they almost never arise...
In the end, if you find that you are completely unable to do sitting meditation, you can very well consider walking meditation, it's an absolutely respectable and effective way to go; also, if you want to practice concentration but are unable to get into it, you may count the breaths while walking until your mind gets into it, and then, with that stability, beginning to sit.
Also, by the way, the more you do walking, the more informal meditation will come naturally; however, also consider that the more you have a strong informal practice, the more the Dark Night will be likely to bleed in your daily life... but also, it's impossible to get EQ or stream entry off retreat without informal practice... in the end, you must consider the options you have and make your own choice.
Hope it helped somehow... bye!
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