What is the meaning of "Achazta Shemuros Einai"?
Rashi: Shemuros is an expression of Ashmuros ha'Laylah. A person wakes from his sleep, and his mind settles and his heart returns to him. I am not so in this night of Galus. My eyes are stuck like a man who sleeps amidst a sealed heart.
Radak: Shemuros are times that he wakens. One who is awake at night is called Shomer - "Shomer Mah mi'Laylah" (Yeshayah 21:11). And so the times of being awake are called Mishmaros and Ashmuros. It says Achazta, as if You held my eyes, which were always awake, and I do not sleep due to the many afflictions of my heart.
Radak citing R. Moshe ha'Kohen: Shemuros is an adjective for the eyelids; they guard the eyes. It is as if You held the eyelids that they not close, and I will not sleep.
Malbim: It is as if due to the great weakness, he reached the gates of death and he is Goses (close to death; most Gosesim die). The eyelids, which guard the eyes, closed.
Why does it say "Nif'amti v'Lo Adaber"?
Rashi: The afflictions that I see agitate my heart, and there is no speech in me.
Radak: This is like "va'Tipa'em Rucho" (Bereishis 41:8). I am awake at night and think about my afflictions, and in the morning I am broken and I cannot speak.
Malbim: My Ru'ach is so agitated that I cannot speak, like a Goses when the Nefesh leaves; he cannot see or speak.
