I have a vertebra that tends to slip out of alignment. Regular visits to my chiropractor keep it in place and prevent too much discomfort, but when I’m on retreat my back sometimes gets so painful that I have to lie down to meditate.

When I first had to do this on retreat, the posture that was suggested was the Alexander semi-supine position, where you lie on the back, with the knees bent and the feet flat on the floor, and the head raised on a cushion.

This is comfortable, but it’s very hard to stay alert in this position, and I’d tend to fall asleep. Even if I …