I will give an example from my experience. When I maintain a meditative streak, and have been careful about my diet, my meditation at times deepens. When I am practicing Spiritual Heart Meditation (in a sitting posture) this way, sometimes the body can shake left and right, forward and back quickly or spiral around widely. The breath can sometimes quicken on its own as if to increase the build up of energy. If the meditation becomes really intense, the body is as if it is shaking/trembling, but I think this is a faster version of the movements when the meditation is less intense.
I had seen in a video of Lincoln Gergar, practicing the same meditation (in a very deeply surrendered state) that he was shaking very rapidly in the whole body and at some point I think he got into Soul Travel. I looked around for this video but couldn’t find it because there are thousands of videos and it has been a while I watched it. During the video he was channeling and he was instructed to trust during the experience and he kept channeling without losing concentration and in the end his body slumped forward at the climax and I think he got into Soul Travel there, looking as if he lost consciousness in the body for a few minutes. He came back after a few minutes, as far as I remember. (I only saw this type of losing consciousness in that video among hundreds of his videos that I watched. Otherwise, he is always fully present in his videos)
If the shaking happens only in your meditations, I would think that it is a result of energy working through your body, to expand its capacity.
We are always guided from within. It is important to practice a meditation that connects you with this guidance. Then you can intuitively adjust your practice. For example: I am experienced with connecting with my spiritual heart because I have been practicing this type of meditation mainy. When I was following a guided meditation by Akahi (a breatharian teacher), he was guiding a rapid breathing exercise in a YouTube video. I followed his guidance up to a point and when I started feeling dizzy, I intuitively knew that my capacity was being reached so I let the breathing stop and remained breathless naturally for a while. He continued his rapid breathing for a while more and he stopped, too. This is an example of prioritizing inner guidance over the external guidance, and I think it is the best approach, if you are able to connect with your inner guidance.
Be careful about your energy capacity. If you have eaten heavily, or unhealthily, I wouldn’t advise going into intense meditations quickly. Food affects our energy capacity. Eating light and as healthily as possible as long as possible will make your meditations which are working on your energy system much more fluent. However, whatever you have eaten, meditation will still benefit you. Don’t force meditations with your mind, always use your common sense, connect with your higher intelligence as best as you can and practice that way. You don’t need to get scared, just trust your inner knowing and be receptive to its guidance to the best of your ability and it will be fine.