Is a wife sinful if she feels distressed when her husband sleeps next to her, so she moves to another room after seeking his permission, knowing that she used to sleep peacefully at the beginning of their marriage?

As long as the husband gives his wife permission to sleep in another room, there is no sin upon her. The wife is advised to maintain the prescribed remembrances (adhkar) such as the morning and evening remembrances and those before sleep, and lawful ruqyahs like reciting Al-Fatiha and the Mu'awwidhat (Surahs Al-Falaq and An-Nas), along with frequent supplication (du'a).