4

The Rambam states that when falling asleep, one should start off sleeping on his left side, and then switch to the right eventually, and then just rotate between those two positions for the entire night (without sleeping on your back or stomach).

H. Deoth 4:5:

לא יישן אדם לא על פניו, ולא על עורפו, אלא על צידו--בתחילת הלילה על צד שמאל, ובסוף הלילה על צד ימין. ולא יישן סמוך לאכילה, אלא ימתין אחר אכילה כמו שלוש או ארבע שעות. ולא יישן ביום.

One should not sleep face down or on his back, but on his side - on his left side at the beginning of the night and on the right side at the end of the night. He should not retire shortly after eating, but should wait some three or four hours. One should not sleep during the day.

Are we to view this as some Halachic idea (specifically the starting to sleep on your left side) and therefore it should still be followed nowadays, or are we to view this as a product of the Rambam’s times and was simply the best medical advice back then?

In short, is this view that you must start off sleeping on your left side and then only sleep on your sides for the whole night have a source in Halacha, or is it simply the medical advice of the Rambam?

And further, if it’s medical advice does it need to be followed today?

10
  • If I remember correctly, it is a means to protect against seminal emission which comes when lying either on one's front or back.
    – Dov
    Commented Oct 25, 2022 at 18:05
  • @Dov ahhh that does actually make sense. But I’m more concerned with the “starting on the left then switching to the right.” Because like every time I go to sleep I always make sure to start on my left but sometimes it’s annoying because it’s simply uncomfortable and I need the right, so I was wondering is this view Halacha or just some medical advice or something Commented Oct 25, 2022 at 18:15
  • 2
    Just some historic context: It is worth bearing in mind that in the pre-industrial era, biphasic sleep was the norm. As a function of modern lighting, work schedules stretching into the night, etc. we are now accustomed to monophasic sleeping. The context in which the Rambam wrote this is likely one wherein people naturally arose for a period in the night, so if they went to bed for the first sleep session on one side and naturally awoke and went to bed again some time a bit later, the exhortation is to change sides. Commented Oct 25, 2022 at 19:18
  • @CuriousYid where did you get this part from: "and then just rotate between those two positions for the entire night" ? Commented Oct 25, 2022 at 20:42
  • 1
    @CuriousYid assuming that it is a medical statement (rather than a restatement of binding Hazalic legislation), then that determination would be made by light of whatever the best contemporary medical practice advises. I am not a doctor, but from what I understand there are health benefits to sleeping on both sides, but that generally the benefit is greater on the left. This may be different however for individuals with specific health issues (digestive, cardiac, etc.) and so of course a decision ought best be made in consultation with ones physician. Commented Oct 26, 2022 at 19:19

2 Answers 2

4

is this view that you must start off sleeping on your left side and then only sleep on your sides for the whole night have a source in Halacha, or is it simply the medical advice of the Rambam?

R. Qafih suggests (commentary on H. Deoth 4:5[7]) that the formulation of this halakhah is based on בריאות (health considerations) whereas his formulation in H. Issure Biah 21:19 is based on Nidda 14a.

H. Issure Biah 21:19

אסור לאדם שיקשה עצמו לדעת, או יביא עצמו לידי הרהור; אלא אם יבוא לו הרהור--יסיע ליבו מדברי הבאי והשחתה, ויפנה לדברי תורה שהיא "איילת אהבים, ויעלת חן" (משלי ה,יט). לפיכך אסור לאדם לישן על עורפו ופניו למעלה, עד שיטה מעט כדי שלא יבוא לידי קישוי.

It is forbidden for a person to intentionally cause himself to have an erection or to bring himself to [sexual] thoughts. If a [sexual] thought comes to his mind, he should divert his heart from profligate and destructive matters to the words of Torah which are "a beloved hind, arousing favor." For this reason, it is forbidden for a person to sleep on his back with his face upward, Instead, he should turn to the side slightly so that he will not develop an erection.

Note that the difference in formulation here concerns your primary question, which concerns the turning over from right to left. It would appear that this specific aspect is indeed medical advice based on the Rambam's understanding of the field in his era. In Dov's answer he cites the שבילי אמונה of R. Meir ibn Aldabi who also maintains that this practice is born of the then extant medical knowledge. Suffice to say, ibn Aldabi's description of the biological functions is not current. Which naturally leads us to your remaining question:

if it’s medical advice does it need to be followed today?

The Rambam in H. Deoth 4: states:

כל מקום שאין בו רופא--אחד הבריא ואחד החולה, אין ראוי לו לזוז מכל הדברים שאמרנו בפרק זה: שכל אחד מהן, לאחרית טובה הוא מביא.

Where there is no doctor available, neither the healthy nor the sick man should budge from all the directions given in this chapter for each of them ultimately brings to a beneficial result.

This means that the Rambam maintained that these medical prescriptions were not absolute even in his own day, and and that they ceded to the medical advice on the ground in relation to one's own health in consultation with a doctor. How much more so, where the state of medical knowledge has changed between his time and ours that these statements ought not be taken as absolutes. Furthermore, his son Rabbenu Abraham (who generally did not deviate from his father's path) taught ( מאמר על דרשות חז"ל ):

לא נתחייב מפני גודל מעלת חכמי התלמוד ותכונתם לשלמות תכונתם בפירוש התורה ובדקדוקיה ויושר אמריהם בביאור כלליה ופרטיה, שנטען להם ונעמיד דעתם בכל אמריהם ברפואות ובחכמת הטבע והתכונה, [ולהאמין] אותן כאשר נאמין אותן בפירוש התורה, שתכלית חכמתה בידם, ולהם נמסרה להורותה לבני אדם, כעניין שנאמר "על פי התורה אשר יורוך" וגו'.

We are not obliged, on account of the great superiority of the sages of the Talmud, and their expertise in their explanations of the Torah and its details, and the truth of their sayings in the explanation of its general principles and details, to defend them and uphold their views in all of their sayings in medicine, in science and in astronomy, or to believe them [in those matters] as we believe them regarding the explanation of the Torah… we find that they made medicinally related statements in the Gemara which have not been justified or validated...

The Maimondean approach does not see Hazal as being inerrant in scientific/medical matters, and therefore where their medical prescriptions are found to be incompatible with the contemporary understanding, we do not follow them. This approach followed to its logical conclusion would imply that, all the more so, where the Rishonim erred in their medical understanding, basing themselves on Galen, Hippocrates, et al. we would not be bound by their medical prescriptions and rather ought defer to the contemporary understanding of medicine.

To conclude, whether one ought sleep on the left or right, and whether one ought switch halfway through the night, is a medical question best answered by a modern practitioner of medicine (preferably your own doctor, familiar with your unique constitution), rather than left to the Rambam's prescription. And that doing so, is in perpetuation of the Rambam's larger halakhic methodological prescriptions.

3

The Rambam you are referring to can be found in Hilchos Deos 4:5:

לֹא יִישַׁן אָדָם לֹא עַל פָּנָיו וְלֹא עַל עָרְפּוֹ אֶלָּא עַל צִדּוֹ. בִּתְחִלַּת הַלַּיְלָה עַל צַד שְׂמֹאל. וּבְסוֹף הַלַּיְלָה עַל צַד יָמִין. וְלֹא יִישַׁן סָמוּךְ לַאֲכִילָה אֶלָּא יַמְתִּין אַחַר אֲכִילָה כְּמוֹ שָׁלֹשׁ אוֹ אַרְבַּע שָׁעוֹת. וְלֹא יִישַׁן בַּיּוֹם

A person should not sleep on his face or on his back, but rather on his side. At the beginning of the night [he should sleep] on his left side and at the end of the night, he should sleep on his right side. He should not sleep close to [the time of his] eating, but rather should wait three or four hours. And he should not sleep during the day.

This Halacha is based on a Gemara in Niddah 14a:

ריב"ל לייט אמאן דגני אפרקיד איני והאמר רב יוסף פרקדן לא יקרא קרית שמע קרית שמע הוא דלא יקרא הא מגנא שפיר דמי

Rabbi Yehoshua ben Levi would curse one who sleeps lying on his back [aparkeid], as this might lead to a seminal emission. The Gemara asks: Is that so? But doesn’t Rav Yosef say: One who is lying on his back may not recite Shema? From this it may be inferred that it is only Shema that one may not recite in this position, but to sleep lying in that position is permitted. (Sefaria translation and notation)

Rashi explains there that the problem is when lying on his back he may have an erection in the night while sleeping and whilst in this position his hands may come to rest on his private part thereby warming it and causing his to have a seminal emission.

It is likewise codified in the Shulchan Aruch, Even HaEzer 23:3 where it writes:

It is forbidden for a man intentionally make himself have an erection or to cause himself to think about sex. Rather if he thinks about sex he should remove himself from vain things and go to the words of Torah which is like a beloved doe and a graceful deer. Therefore it is forbidden for someone to sleep on their back with his face up, rather he should lean to the side so that he doesn't come to have an erection.

As to why the left side first, the commentaries on the Rambam explain the reasoning. In the Chiddushei Mayim Chayim and Pri Chodosh it writes:

בתחילת הלילה על צד שמאל. הטעם כתב בס' שבילי אמונה כדי שיהא הכבד שהוא בצד ימין על האצטומכא ויחום אותה בחמימותו וימהר עיכול המאכל

Begin the night on the left side - The reason is written in the Sefer Shivili Emunah - so that the liver, which is on the right side, will be on the stomach1 and heat it with its warmth and the digestion of the food will speed up.


1Refer to the Shevili Emunah here (3rd paragraph) for a good biological rundown of the "אצטומכא"

1
  • Two things. First of all, I see the problem with lying on one’s back based on the Gemara (though it does seem that Rav Yosef implies that one is allowed to lie on one’s back but just simply can’t say Shema so clearly the notion is up for debate). But my question is what’s the Rambam’s source for not lying on your stomach? And my second question is that your answer (although it taught me new stuff so thank you) didn’t answer my further question of whether the lying in your left first is Halacha or simply a medical recommendation Commented Oct 26, 2022 at 10:34

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .