In contemporary Insight Meditation, we often include the expanded postural guideline that lying down is a fine meditation posture if sitting isn’t available for your body. This is a good instruction, and I think it’s really skillful to include laying down in one’s vocabulary of postures, including for formal meditation. Accessibility is a prerequisite for practice.
That said, I want to reflect on the phrase “setting the body upright” that appears in the texts as a preliminary to meditation. The Pāli is “ujuṁ kāyaṁ paṇidhāya,” and ujuṁ is the adverb form of uju, meaning “straight direct; straightforward, honest, upright.” The definitions of the word make it clear that it has the same somatic metaphor as the English “upright,” which we use to mean moral clarity as well as having the spine extended in the vertical plane.
In both European and south Asian cultures there are endless references to uprightness being/showing a moral strength and slouchiness and reclining as being weaker. This is worth critique as an ablist bias. It is also obvious that different postures condition different energetic and cognitive experiences. So it’s important to be careful to say that sitting upright isn’t “better” than lying down, but still to feel into the power of upright posture in practice.
Embedded in our need to defend non-upright postures as effective for meditation is the trauma of the post-industrial body, which for many of us precludes sitting comfortably upright without back support. I think there are scores of reasons why Euro-American practitioners struggle in meditation, often working with beginner instructions for our whole lives, and I suspect that inability to sit upright is one of them. Along with legacies of trauma in our families, communities, and cultures, patterns of collapse in the body from chair, car, couch, & keyboard have a role.