Is It Necessary to Stand for the Vidui of Keriat Shema Al HaMitah?

Shalom, and thank you. 

One should stand when reciting the vidui of Keriat Shema al HaMitah. 

Sources: Based on what the Shulchan Aruch writes regarding the laws of Yom Kippur (siman 607, seif 3), one must confess while standing. The Mishnah Berurah (sk"k 10) writes that this is a greater expression of submission and one thereby confesses with a full heart. In Kaf HaChayim (seif 23), he cites the Yafeh Lalev, who notes that we find in Sefer Nechemiah (chapter 9, verse 2), "They stood and confessed their sins." This is stated explicitly as well regarding the vidui of Keriat Shema al HaMitah - in Shaar HaKavanot (Derush 5 of Derushei HaLaila), in the glosses of Mahara Azoulai zt"l on Levush, Orach Chayim (siman 239, sk"k 1), in Yalkut MeAm Loez Bereishit, part 2 (page 658), and in Yesod VeShoresh HaAvodah (Shaar HaBekhorot, chapter 12). 

With blessings, Hillel Meirs