1)
Why does it say "Ki Sav'ah v'Ra'os Nafshi"?
1.
Rashi: This discusses Keneses Yisrael. Radak - this is like "Hisbi'ani va'Merorim Hirvani La'anah" (Eichah 3:15), "Seva Kalon" (Iyov 10:15). Fullness of a matter is satiation. Ra'os are the afflictions of Galus.
2.
Malbim: All my life were only evils; I was satiated from them.
2)
Why does it say "v'Chayai li'Sh'ol Higi'u"?
1.
Radak: I am close to death.
2.
Malbim: This is the opposite of [Avraham], about whom it says "va'Yamas Zaken v'Save'a" (Bereishis 25:8).