The Balance Resting State is one of the procedures used by the Alexander Technique to restore well-being and allow a person to come back to a neutral state of non-reaction or a chosen reaction. For that, the pupil will allow her/himself to stay for 15 to 20 minutes in the semi-supine position without attempting to move or achieve anything in particular.
You can lie down on a table, a carpet, or even on the grass!! Use a book underneath your head. To determine the height needed, use the length of your thumb or better, ask your Alexander Technique teacher what the ideal book thickness is to use. That varies according to the person and even the time of the day.
The whole idea of being in this position is to bring yourself into a state of lower stress, anxiety, and pain. The way to achieve it is not through forcing or aiming but just allowing yourself to be there and notice what you notice.