Every night is a minor death,
the death of another day,
as we advance towards
the day of our ‘redeath’.
In the Seyyā Sutta, which is the discourse on ‘Lying Postures’, the Buddha taught that there are the four following ways of lying down.  There is lying flat on one’s back, which is how a corpse would lie.  There is lying on one’s left, which is how those seeking pleasures would lie.  There is lying on one’s right, which is how lions would lie, with one foot on the other.  There is lying of the realised ones, free from seeking sense pleasures and unskilful qualities, as they enter increasingly deeper meditative concentration. Being literally awakened, both spiritually and physically, the Buddhas do not really ‘sleep’, while they manifest ‘sleeping’, which is more of ‘resting’ of their bodies, while ‘recharging’ their minds.
Although the Buddha did not say so directly above, as depicted in Buddhist imagery in terms of sculptures and paintings, he usually lies on his right, in the lion’s posture  physically, while having his mental posture as stated in . As such, Buddhists are generally encouraged to lie down similarly, which is supposedly more skilful for resting the body and cultivating the mind, (while it is considered alright to fall asleep while doing so, which this leading to more peaceful sleep). However, instead of staying put in one posture, most of us tend to toss and turn in the course of the night — exactly because we are somewhat restless, not restful enough in body and mind!
That said, it is still ideal to sleep every night with physical posture  and mental posture . Meditative concentration can be practised silently with chanting too, including with mindfulness of the Buddha’s name. Even though it is challenging to lie down still as proposed throughout the night, ultimately, in terms of priority, it is mind over matter. Although a better physical posture facilitates a better mental posture, it is more crucial to have a better mental posture than a better physical posture. What important is to rest as peacefully as we can, and to have some practice while doing so when possible. To keep tossing and turning to retry the ideal posture after giving up might not lead to much rest!
While practice does make perfect eventually, we cannot force others to lie down in the ideal posture when they are sick and dying, especially if they find it uncomfortable. While sleeping can be used as a daily (or rather nightly) activity to ‘rehearse’ for our dying moments, our karma might not allow us to depart in our preferred posture later. Bearing this in mind, what matters most, again, is our state of mind. After all, when it is time for our minds to depart from our bodies, our bodies (and their postures) should be readily renounced, no longer on our minds. It was after all, probably with attachment to our bodies to some extent in our previous lives, that we return trapped, still not liberated from our imperfect forms.
Every day is a minor birth,
the birth of another day,
as we advance towards
the day of our rebirth.