During sleep, the neck stays in the same position for 6-8 hours — so a bad position can have a longer-lasting effect than any single bad posture moment during the day. Sleeping on your back or side keeps the neck more neutral than sleeping on your stomach, which is generally the least recommended position since it keeps the head turned to one side for hours. Pillow choice (see related article) should be considered together with sleep position — for example, side sleepers need a higher pillow to fill the shoulder gap. If you frequently wake up with neck stiffness, both your pillow and sleep position are worth reviewing.