The Constructive Rest Procedure is another name for the Lying Down Procedure, also known as Semi Supine or the Active Rest Procedure, as taught in Alexander lessons. (I wonder how many more names this procedure will be given in the future!)
The procedure is an invaluable tool to use to recharge your batteries, unwind, look after your back and to become more aware of your body use and mind-body connections. It is practised in a semi-supine position - ideally every day, on a firm surface with some books to support the head. In this photo you can see a student lying on my Alexander table during a lesson. Generally, people use this whilst lying on the floor when practicing at home or at work, rather than on a soft surface like a bed which does not give enough support.
Further details about how to use this are to be found in my notes on using the Lying Down Procedure but you really need to learn this from an AT teacher first, so that you understand how best to use it.