What's wrong with Mildred and what effect does the contra-sedative have on her?
I'll answer part of your question concerning Fahrenheit 451. Mildred overdoses on sleeping pills one night, and Montag finds her after he comes home from his shift at work.
The technicians that pump her stomach are so matter-of-fact and nonchalant about saving her life, that Montag realizes they must do this all of the time. Mildred's overdose and the nonchalance of the technicians make Montag further question his existence and the society he lives in.
Millie doesn't remember anything the next morning, and is terribly hungry. This, of course, metaphorically suggests the emptiness of her life and existence.
Physically, what is wrong with Mildred is that she took too many sleeping pills the night before. We do not know if this was on purpose or not. But she had to have her stomach pumped and she had to have the contra-sedative to counteract the sleeping pills.
The effect that the drug has on her is to make her very hungry in the morning. She cannot figure out why she is so hungry. And that points to what's really wrong with her. She has no feelings, she isn't really aware of her life. She doesn't even know that she took too many pills. She might as well be dead.