There are only four ways a person may lie in bed, face up, face down, or sideways.
先説仰臥，自從有脊椎動物以來，人類大概是惟一會用仰臥的動物。小貓小狗有時候四腳朝天和主人玩，可是極少這樣睡覺。對人類來說這是一個極不衛生的姿式。可是也是最常被人用的姿式。脊椎動物一向是以脊椎為主，從魚類開始一直到狗貓牛羊，都是把內藏之類的挂在下面好像挂在曬衣桿上似的。到了人類就把小孩兒面朝上放在搖籃裏。那麽從小到大就仰睡了 。即使是小孩兒也要注意，大人要把小膼袋時常左右的動一動。不然的話就會有個張點頭,王扁頭之類的啦。成人仰臥則可能有小舌頭向後落下的可能。同時鼻腔的分泌物本來應該向前進入食道的，可是在仰臥的情形下就往後跑到氣管去，這就是病人仰臥可能轉成肺炎的原因。一般都會是把病人或是老年人仰臥放在床上，其實那是一最不好的。要是床太軟了再加上枕頭太高了就會形成駝背。要是床硬就應該要在腰眼底下以及腿底下墊高一點。Let’s first talk about sleeping facing up. Ever since vertebrates appeared on earth, human beings are probably the only ones who can sleep on their backs. Kittens and puppies may play with their masters lying on their backs but they don’t sleep that way. Even for human beings, it is an unhealthy posture, I would say. For vertebrates, from fish till lamb or dogs, the spine is like the support of a suspension bridge. Everything hangs from it. Now, humans have started to put their babies in cradles facing up and they got used to sleep facing up when they grow up. Even with kids, parents should be very careful not to let the baby stay with the head in the same position too long. Otherwise a squashed head may be created. For adults, the back of tongue tends to fall back while going horizontal facing up. Besides, the throat is supposed to drain forwards into the esophagus. Facing up will cause it to drain into the air pipe into lungs. That is why people in sickbed or elderly people in bad facing up may catch pneumonia. This is the regular hospital practice, which is actually not healthy. Additionally, in this posture, if the bed is too soft and/or the pillow too high will cause hunch back; if the bed is too hard, one must use cushion below the waist and under the knees to avoid injury.
俯臥依上面所說的應該是最自然的。獅子，老虎，牛，羊，甚至于狗，貓都是這麽睡的。在電影裏我們常常看到小女孩，或者小女生伏臥在床上把小腳翹起來，還給朋友通電話，或者玩手機，看書之類的。可是現在要俯臥睡覺 就有兩個困難。第一就是我們的手腳已經不能像牛羊那一樣卷在身子底下了。第二就是:我們的頭已經只適於直立的時候向前看。要是趴著睡那臉就埋在枕頭裏頭了。所以需要特制的枕頭，再不然就得把頭向左或者向右歪著睡,很不舒服。From what we said about thing hanging down from the spine, you would say facing down is the right way. In fact, lions, tigers, cattle, dogs, and cats all sleep that way. We also see in the movies, it is fashionable for the “girls” talking to their friends, playing cell phones, reading … in bed on their stomachs. Well, there are problems sleeping this way. First of all, our arms and legs can no longer be tucked under the body the way the animals do. Secondly, Homo Erectus has enjoyed standing up so long that the face is perpendicular to the spine as opposed to be in line as those animals have. To lie facing down, one would have to have some special pillows or supports to allow breathing very much like the type attached to a massage table.
Sleeping on the side is quite natural. People like to curl up, or, call the fetus position. When you take this position to bed, it is naturally “sleeping on the side.” It makes no difference whether it is on the left or right. Maybe on the right gives less pressure to the heart.
Now, about the bed. I often heard the saying that hard bed is good for people, especially elderly. This talk is probably related to sleeping facing up because bed too soft might be one of the causes of hunchback as mentioned above. Also, as mentioned, even for that, keeping the curvature of the spine and keeping the angle of the legs to the spine is to be considered.
So, should a bed be hard or soft. Well, like anything else, it is not a binary question, not an either/or question. The answer must lies in between. Say, the structure of the human body is wider at the shoulders and hips but narrower in between. Put such a body on a hard bed sideways is like putting a dumb bell on a board, creating two contact point. Gravity is to pull the middle part down and causing the problem of S-shaped spine. Those who have this problem often say it is because of inheritance. In the nmwean while they insist proudly on sleeping on hard bed, without knowing that was to blame.
我知道有好幾個人他們都說大腿外面有一塊皮膚漸漸失去知覺，再問一問,就發現他們都是側睡,都是硬床,都是睡在失去知覺的那一邊。要是我現在說那是因為睡硬床。你一定會說我亂下結論,說我誤用統計,或者說我統計的材料太少. 好,我現在什麼都不說. 你們有空自己想想好了。
I know of a few people who have slowly losing feelings on a patch of skin on the out side of one upper leg. Upon asking they all say they sleep on that side and that they use hard bed. Now, if I say that were the reason, you would accuse me of making false conclusions; using statistics wrongly; or having to little data. OK, I will say nothing. When you have time, think about it a little.
以前的軟床常常是中間㡳四面高.好像個吊橋, 或者平碗似的.當然也對人體不好. 最好的床是睡在上面不改變身體的形狀。那麼說在太空無重力的情形下應該是最好的了.可是誰每夜能到太空去睡呢？第二好是浮在水裏，因為水是不會改變任何東西的形狀的,浮在水裏的東西各處表面上所受的壓力都是完全一樣的。”水床”的設計是根據這個原理,可是也不能做的十全十美. 現在做床多是用一種特殊的床墊,多受壓力的地方就多凹進去一些.這樣就會減少改變身體形狀的可能性。這種物質中文叫做乳㬵,英文叫 Memory Foam. 非常好用. (Memory Foam 是發展太空科技的的時候發明的).現在市場上有一種用這種材料做的三寸厚的床墊，可以放在普通床上用.這 是非常理想的.
Traditional “soft beds” were to make the center part “softly” suspended form two ends or four sides. That would make a suspend bridge type of a structure, could not be of much help. Ideally it is to let one sleep without changing the body shape. That can be achieved probably only by sleeping in outer space. Well, who wants to go to outer space every night! The second best way is to be floating in water. That is why the space program train the would be astronauts in water. Water pressure presses from all directions evenly. Problem is to find a way to breath. The waterbed is designed according to this principle but is still not ideal. Well, nothing can be perfect. Recently people make beds with Memory Foam. this thing caved in at the point the pressure is high. At rest of the place it keeps shape to maintain pressure towards the rest of the body. At this time, I would guess, a 3 or 4-inch cushion on a hard bed may be the best we have got.