Why did he say "Habitah Aneni Hashem Elokai"?
Radak: This corresponds to "Tastir Es Panecha Mimeni." You, Hashem, have the ability to save me, and You are Elokai, and judge my case from my enemies.
Malbim: This corresponds to when Hashem 'forgot' him. He asks Hashem, look at me with Your eye of Hashgachah and answer me!
Why did he say "Ha'irah Einai"?
Malbim: His spiritual eyes are dark, and his soul sleeps the sleep of spiritual and intellectual death. Real life is spiritual, intellectual life when he goes in front of Hashem - "v'Atem ha'Devekim ba'Shem Elokeichem Chayim Kulchem ha'Yom" (Devarim 4:4). Life of sensation and motion is animal life; it is death for the Divine Nefesh.
Why did he say "Pen Ishan ha'Maves"?
Rashi: Death is called sleep - "v'Yashnu Shenas Olam" (Yirmeyah 51:57).
Radak: I am in the darkness and sleep of exile and afflictions; before I sleep the sleep of death, "answer me and enlighten my eyes"!
Malbim: Refer to 13:4:2:1.