There are four levels of mental absorption that can be attained while prostrating with the mind focused on movement. The first is to pay attention to all aspects of motion of the body, each and every detail, while directing that motion. At the second level you do not pay attention to all the details, but you are aware of directing the body. Third, you do not direct the body or think of the body as being yours, yet you still watch it prostrate. Fourth, you are not aware of a body or a being moving; nonetheless, prostrations continue. There are two variations of the fourth level. One is when a person freezes, either motionless in an up or down position. The body and mind have separated so the person cannot move, but it is not true samadhi. The better variation is when the body continues to make prostrations even though the mind has stopped moving. This is true samadhi.
The samadhi level is not easy to get to. Here at the Ch'an Center, I've only seen a few people get even to the lesser version of the fourth level. I have also seen a few people get to the third level, where they say that it seemed as if they were watching someone else.
So far I've been talking about making slow prostrations. Even when prostrating slowly you may still have a lot of wandering thoughts. If you cannot calm your thoughts, then you can do fast prostrations. This usually lessens wandering thoughts, especially when coupled with reciting the Buddha's name.
I've talked about at least four varieties of prostrations: prostrations of respect, prostrations of gratitude, prostrations of repentance, and prostrations as samadhi practice. Regarding the first three kinds of practice, you cannot do prostrations and maintain those mental attitudes for a long time. You can make a few prostrations with gratitude but then that mental state fades and disappears. The same is true for attitudes of respect and repentance.
Repentance prostrations usually include some type of liturgy that is recited before or after the prostration session. The liturgy expresses sentiments of repentance. The main part of the practice, however, is prostration. while prostrating, do not accuse or blame yourself or indulge in self-pity. Do not maintain those sentiments in your heart. Once you repent, put it aside and prostrate.