What is the meaning of "Eshtolelu"?
Rashi: This is like Hishtolelu (became crazy), like "Molich Yo'atzim Sholal" (Iyov 12:17). We find that "Eschaber Yehoshafat
Why does he say that they forgot? Did they previously know that Hashem will destroy them? Until now, Sancheriv conquered every nation that he fought, including the 10 tribes! (PF)
What is the meaning of "Namu Shenasam"?
Rashi: They slept. Namu is like Tenumah.
Radak: They slept the sleep of death. They had no power to fight, as if they slept their future sleep of death, i.e. as if they were dead.
Why does it say "Lo Matz'u
Rashi: They did not have their strength when You came to exact payment from (punish) them.
Radak: Their Giborim were not able to fight.
Malbim: The verse depicts as if when the Tearer came against them, they did not have hands to fight. How did this happen?!