We should lie down to listen to music much more often. Gravity pulls away the thought and frown lines, smoothes the intellectual tracks and folds on the face, while you feel the blood in your head pumping lushly to dreamier parts of your brain. Joanna MacGregor’s If-A-Tree festival at the Royal Opera House this weekend may well be hitting some fey bases along its way, but Earthrise: The Lying Down Concert - was a spectacularly enjoyable opening event.