1)
What is "Shenas l'Einai"?
1.
Radak, Malbim: It is a fixed sleep. The Sov at the end of Shenas is in place of a Hei. The same applies to "Sefas Lo Yadati Eshma" (81:6) and similar verses.
2)
Why did he say also "l'Af'apai Tenumah"?
1.
Radak: The matter is repeated in different words.
2.
Malbim: This forbids even a light sleep [in his house].