I have treated myself to one of these, and have used it for the first time today, laid on the floor, it also heats up, bliss, only problem I have is where do I put my hands, while its going through the motions
Yours is one of those questions where my first thought was "I haven't got a clue" but that was then followed up by one of "So let's find out". To that end I search Youtube for 'massage mat' and most videos seem to show the user simply resting their hands on their tummy. e.g.