About This Answer
Must the back stay straight in meditation? A meditator finds that when practice deepens his back curves by itself, and straightening it disrupts his focus. Ajahn Dtun, through an interpreter, says that when sitting with others in a public place it is normal to keep the back straight, especially if the mind is not yet peaceful. Practising alone at home, though, the mind matters more than the body: if the mind is still focused while the body leans or sways, pay it no attention and stay with the focus.
If attention goes to the body, mindfulness is not broken but redirected, "sending the mind out," and one simply brings it back to the present. Irritation at the mind wandering is unnecessary; until it is firmly established, movement is normal.
Asked about walking from morning to 3 p.m., he clarifies that after the meal he alternated, walking until tired, then sitting until sore, then walking again.