Question: Does the woman fall into sin if she refuses her husband when he calls her (to his bed) if she is suffering from a fleeting mental lapse, or she is ill and suffering from pain?
Response: It is obligatory upon the woman to respond to her husband if he calls her to his bed. However, if she is ill due to a mental lapse and is unable to face her husband, then in this situation it is not permissible for her husband to request her (to satisfy his (sexual) needs) as the Prophet (sal-Allaahu `alayhe wa sallam) said:
«There is to be no harm and no causing of harm».
And it is upon him to restrain himself and seek to satisfy (himself) with his wife in a manner which will not cause any harm (to her).
Shaykh Ibn ‘Uthaymeen
Fataawa az-Zawaaj wa ‘Ishratun-Nisaa. – Question 72, Page 103