What is the reason behind the Buddha's advice to lie down on the right side "in the lion's posture?" Why not on the left side for example?
"And how is a monk devoted to wakefulness? There is the case where a monk during the day, sitting & pacing back & forth, cleanses his mind of any qualities that would hold the mind in check. During the first watch of the night,1 sitting & pacing back & forth, he cleanses his mind of any qualities that would hold the mind in check. During the second watch of the night,2 reclining on his right side, he takes up the lion's posture, one foot placed on top of the other, mindful, alert, with his mind set on getting up [either as soon as he awakens or at a particular time]. During the last watch of the night,3 sitting & pacing back & forth, he cleanses his mind of any qualities that would hold the mind in check. This is how a monk is devoted to wakefulness. - AN 4.37


