Dr. Robbins said that a temperature between 18 to 20 degrees is optimal (experts have talked to us about this before) for sleep, and anything higher than that can cause sleep fragmentation and nightmares.
Room temperature is really important when it comes to sleep, she explained, because we want our body temperature to dip low. This dip in core body temperature is associated with sleep onset, and "in experimental studies in warm rooms, or if we put a heating pad under subjects while they sleep, they'll have more nightmares and their sleep will be less restorative," Dr. Robbins said.