“(The Four Positions)
 “Furthermore, when walking, the aspirant discerns that one is walking. When standing, one discerns that one is standing. When sitting, one discerns that one is sitting. When lying down, one discerns that one is lying down. Or however one’s body is disposed, that is how one discerns it.
“In this way one remains focused internally upon the entire body, or focused externally… not clinging to anything in the world. This is how an aspirant remains focused upon the entire body.
 “Furthermore, when engaged in walking meditation, one makes oneself fully alert; when looking near and looking far… when bending and extending one’s limbs… when carrying one’s outer cloak, one’s upper robe and one’s bowl… when eating, drinking, chewing, and savoring… when urinating and defecating… when walking, standing, sitting, falling asleep, waking up, talking, and remaining silent, one makes oneself fully alert.
“In this way one remains focused internally upon the entire body, or focused externally… not clinging to anything in the world. This is how an aspirant remains focused upon the entire body” (Digha Nikaya 22, Maha-satipatthana Sutta, DN 22).
Meditation does not have to be a physically difficult or austere practice. It is possible to practice, not only in the lotus position, but while standing, sitting, walking, falling asleep, waking up, talking or remaining silent. Heck, the Buddha even says that it is possible and advisable to meditate while on the toilet. The key is simply to remain focused on the body and mental states rather than clinging to anything in the world.
Some also find the yoga position known as savasana helpful:
Sotapanna Jhanananda (Jeffrey S, Brooks) describes his own experience using this technique:
“In the yogas Shivasana is recommended. Shivasana is lying flat on the back with legs about shoulder width apart and arms by the sides, with hands about a fist distance from the body, and palms turned up. I have found I can relax deeper in Shivasana than I can in lion’s pose.
The intent of lying down meditation is to relax the body at the deepest level. It is therefore recommended to practice some kind of progressive relaxation method. The classic U Ba Khin Vipassana body scanning method can be effectively modified for this purpose. Simply scan the muscles and tendons for any sign of tension. When tension is found simply relax it. If you cannot immediately relax the tension, then simply observe the tense location as if it were a meditation object. I have found the most tense areas of my body eventually relaxed with enough patience.
Lying down meditation can be practiced anytime. However, as a dedicated contemplative, then such a one would wish to never become unconscious, not even while the body gains its rest at night. Therefore the best times to practice lying down meditation is at the beginning of the sleep cycle.
I have found lying down meditation, especially in Shivasana, is ideal for practicing out-of-body (OOB) practices. So, if you feel that your practice path is sufficiently mature for OOBs, then gaining skillfulness in lying down meditation can only help.”