Immediately his health began to decrease. Fortunately using the movement technique he already came from those monsters and that is the reason he did not get more affected by those poisonous gas.
Wasting no time David began to use health points to recover The lost health. But as you can see the poison affecting him and his health stilp begin to decrease.
Sometime later, the emperor's full body turned purple. The good thing is that the effect of the poison begins to decrease. The Emperor previously did not get that much affected by the poison which is a good thing.
During the time the game character or you should say the emperor begins to feel fatigue. Fortunately as the poison begins to decrease, the fatigue also begins to decrease.
But even with that he almost needed 15 minutes to recover from the poison. David just thinks about what would happen if he faced those Monsters in real life.