1)
What is "Yir'ah va'Ra'ad"?
1.
Radak: Amidst great fear in my heart, my body trembles and shudders. Ra'ad and Palatzos are the same, in different words.
2.
Malbim: This is more than Chil.
2)
Why does it say "va'Techaseni Palatzos"?
1.
Radak: This shows the magnitude of shuddering (it covers me).
2.
Malbim: I was covered with the shock that seizes someone at the time of death.