She has a couple of different reactions worth noting. On pages 41-42, we see these. She first reacts by questioning if he is drunk. He makes more noise than usual and she wonders what the deal is. He is a little forceful about having the light on and won't just comply with her request.
Later, she actually touches him and finds that he is wet from sweating. The sad part of this entire section is that Mildred reacts to Montag's sickness by putting her seashells back in her ears and moving on with her sleep. A true loving wife would probably take care to help manage her husband's comfort. She gives not one ounce of care.