She leaned back, feeling enervated.

Answer: Option D

Disheartened : having lost determination or confidence; dispirited.
Confused : (of a person) unable to think clearly; bewildered.
Saddened : cause to feel sorrow; make unhappy.
Weakened : make or become weaker in power, resolve, or physical strength.
Enervated : make (someone) feel drained of energy or vitality.

Synonym of Enervated is Weakened