He feels alive, invigorated, and completely satisfied. This is the correct option.
While he was next to the flower, Calypso, John Muir, the writer, did not feel hungy or tired -Hunger and weariness vanished- . Then, when the sun set, he decided to come back. However, he felt strong and excited - strong and exhilarated-. He was so happy that he did not care about anything - if never more to feel any mortal care-.
These options are not right:
-He becomes depressed to leave such a beautiful, rare flower. He thinks the flower is beautiful but he does not feel depressed. On the contrary, he feels full of energy.
-He is hungry, weary, and ready to be in a warm house. His hunger and weariness have disappeared. By chance, he finds a house.
-He is relieved that he made it out of the swamp before night. The writer has never got scared. He decides to leave the swamp when the sun sets.