Modality of Prayer: Putting One's Head Down for Tahanun

Gil has started a discussion as to whether one should put one's head down during the supplications following Shaharit and Minha, known as Tahanun, if there is no Aron Qodesh or Sefer Torah in the room. The common practice is not to do so (based, I suspect, upon the medieval Ashkenazic idea that the Torah is an embodiment of God's Name, and that therefore the Shekhinah is present in its plenitude, wherever there is a Sefer Torah).

The Rav זצ"ל's practice was to put his head down irrespective of where he was praying (and I once saw R. Aharon Lichtenstein do so at the airport). The Rav addressed this once (in my hearing) in his shiurim to Masskhet Taanit (in Boston).

He started by referring to the Gemara in Berakhot (34b:

ושוב מעשה ברבי חנינא בן דוסא שהלך ללמוד תורה אצל רבי יוחנן בן זכאי, וחלה בנו של רבי יוחנן בן זכאי. אמר לו: חנינא בני, בקש עליו רחמים ויחיה. הניח ראשו בין ברכיו ובקש עליו רחמים - וחיה. אמר רבי יוחנן בן זכאי: אלמלי הטיח בן זכאי את ראשו בין ברכיו כל היום כולו - לא היו משגיחים עליו. אמרה לו אשתו: וכי חנינא גדול ממך? אמר לה: לאו, אלא הוא דומה כעבד לפני המלך, ואני דומה כשר לפני המלך

On another occasion it happened that R. Hanina b. Dosa went to study Torah with R. Johanan ben Zakkai. The son of R. Johanan ben Zakkai fell ill. He said to him: Hanina my son, pray for him that he may live. He put his head between his knees and prayed for him and he lived. Said R. Johanan ben Zakkai: If Ben Zakkai had stuck his head between his knees for the whole day, no notice would have been taken of him. Said his wife to him: Is Hanina greater than you are? He replied to her: No; but he is like a slave before the king, and I am like a nobleman before a king

The Rav explained that there are two, unique postures in prayer: a) Dignity ('a nobleman before a king) and b) Total self-abnegation ('a slave before the king'). Our daily prayers comprise both. In the Amidah, we stand erect and follow the choreography of a minister or a nobleman before the King. Then, we become slaves before him and cast ourselves down before him (ביטול היש - his phrase).