1)
Which Mesim are discussed?
1.
Radak: Those whom Hashem killed before their allotted time, because they did not recognize in their lifetimes that He is the Master, and did not fear Him.
2.
Malbim: All Mesim. From here until "Ana Hashem Ki Ani Avdecha" (116:16) discusses David's illness. He despaired, and via his Tefilah, Hashem returned him to his strength.
2)
What is "Dumah"?
1.
Radak: It is the grave. The body descends to it, and the Neshamah of a Rasha is lost when the body perishes; it is as if also it descends to the grave. Malbim - there, they are Domemim (silent) and cease from their actions.
