Tatami as a definition is a type of mat made out of rice straws or wood chipboards. For massage it is placed on the floor and a rolled up towel is used as headrest – nothing else needed for a perfect relaxation. The masseuse or the erotic massage usually kneels on the side of the patient and performs the massage in a halfway elevated position.
Besides using it for massage, tatami is also widely used for general relaxation and sleeping as well. There are special beds that have tatami-mat platforms. It is perfect for your back as it keeps your spine in the correct position while sleeping and reduces joint and muscle tension.
As someone from the western world, it feels so much better to be massaged on a tatami then on a generally used massage bed.