Zeus could not hold on any longer.
In order to transport Nyarlathotep, Jiang Lu had to keep his body on the brink of collapse to prevent being controlled and turning into an enemy.
After all, though it was just an avatar, this was still an avatar of the Chief God, and without divine power as an obstacle, Nyarlathotep might become even more powerful than when Yehuhti served as the vessel.
Jiang Lu deliberately lowered Zeus's pain sensitivity to the minimum during the process, but dulling the senses did not mean there was no feeling at all, and the intrinsic fear and despair of watching oneself decay, more than any pain, were something that one would resist.
Jiang Lu had planned to use items he carried to save him after Nodens had sealed Nyarlathotep.
Healing Potion, all-purpose tonics, Holy Water.
With these items, Jiang Lu had confidence that even if Zeus was left with just a breath, he could at the very least prolong his life.
