About This Answer
A meditator describes the whole body rocking like a boat during sitting, and on another occasion feeling the arms come away from the body and even hearing the sound of bones breaking. They ask whether this is a stage of samādhi and what will happen if they continue.
Ajahn Dtun answers that it is both a condition of concentration and a condition of the mind. When the mind becomes peaceful, the body rocking is one form of pīti, or joy. One should simply be aware of it with mindfulness and keep attention on the meditation object.
The sense of the arms coming away is the mind seeing the body break apart, seeing its impermanence. Such experiences arise to teach the mind to let go of attachment to the body, showing that once born it breaks up and is not the mind. He encourages the meditator to stay mindful in the present, knowing that all such phenomena are impermanent. This will not happen to everyone, but the practice is on the right track. Next time, he advises, do not want it to happen again or dwell on past experiences; just keep mindfulness with the meditation.