Why does it say "Hukah cha'Esev"?
Radak: Just like the sun strikes moist grass until it dries, so my heart dried.
Malbim: He depicts himself like vegetation. If the sun strikes it and its power of sprouting (Nefesh ha'Tzome'ach) is stricken, it withers and dies. It will no longer nurture its food (moisture of the ground). So my heart, the abode of life, was stricken like grass and dried.
What is the significance of "Shachachti me'Achol Lachmi"?
Radak: Amidst great affliction, I forget the food. Biology teaches that bodily life depends on the heart; it is the fundamental heat of the body. From it, it spreads to the entire body. The brain is cold and moist. This balances the heat and dryness of the heart. If not for food, the body's heat and the air surrounding it would dry the moisture of the body. Food and drink restore the moisture that it loses due to the heat and air. If one does not eat, the heart dries and he dies - "Yavesh ka'Cheres Kochi" (22:16).
Malbim: Hashem established a certain matter in the stomach that arouses hunger and stimulates the person to eat. This power has been forgotten [in me]; it no longer arouses appetite.
