When Montag returns home in the beginning of the novel, he finds his wife Mildred almost dead from an overdose of sleeping pills. After an emergency crew comes and saves her -- shocking in their callous approach to medical care -- she wakes up the next morning and claims to have no memory of the incident:
"You took all the pills in your bottle last night."
"Oh, I wouldn't do that," she said, surprised.
"The bottle was empty."
"I wouldn't do a thing like that. Why would I do a thing like that?" she asked.
(Bradbury, Fahrenheit 451, Google Books)
Montag suspects that Mildred is unhappy in her mind, but doesn't realize it because she is so well-conditioned by TV and society. For her part, Mildred never mentions it again, and continues to be obsessed with the "family" in the TV screens, showing that even if she had attempted suicide, her focus and willpower is not strong enough to continue trying. As an unconscious reaction, taking the pills could be a mental rebellion against society; as a conscious decision, Mildred could have experienced a moment of clarity, and felt despair at her meaningless life.