Rashi: The Ru'ach of a man who is a Gibor, and does not worry in his heart; he receives everyone who comes to him with Simchah and love. He can 'finance' his illness - his strength will not depart from him.

R. Yonah: Man's Ru'ach bears bodily illness - "Lev Same'ach Yeitiv Gehah" (17:22).

Malbim: The Ru'ach carries the body. Also if the body is ill, the Ru'ach has power to 'finance' the illness, and give to the body strength to bear it and re-invigorate itself.

R. Yonah: When the Ru'ach worries and sighs, who can console it and help it?! The Ru'ach consoles and bears bodily illness, but the body cannot console the Ru'ach from its illnesses, i.e. worry. The verse warns not to let worry rule over the Nefesh, rather, to strive to trust in Hashem and rely on Him.

Sha'arei Teshuvah 4:12: A Ba'al Teshuvah should always groan with a bitter heart, and put this in place of afflictions. When the body is ill, the Nefesh bears its illness. This is like "Mi Mechalkel Es Yom Bo'o" (Mal'achi 3:2). It helps the body and sustains it, when it talk to his heart and consoles him to accept and suffer. However, when the Nefesh is ill from agony and worry, who will bear the body and sustain it?!

Malbim: If the Ru'ach is ill, who will carry it? Then the illness reaches also the body - "v'Ru'ach Neche'ah Teyabesh Garem" (17:22).