Question

The noxious fumes of ammonia and bleach filled her nostrils and overwhelmed her; she hit the ground with a loud thwack.

Answer 1

In this instance, noxious probably means "overpowering" or maybe even "poisonous." Ammonia and bleach are highly toxic substances. They have very strong odors and can be harmful to the respiratory system.

Answer 2

It shows that Ivan evades death at the end because his illness has been healed.