Strange heat in head at night

My 80 year old Mom, who has hypertension, has been experiencing strange sensations at night. After she has fallen asleep, she says she's woken up by her head and neck being very hot. She doesn't have pain, headache or fever with this, and the heat is only in her head and neck, nowhere else in her body. It has caused her great difficulty because it wakes her up and then she can't fall asleep again making her very tired during the day. She has tried taking one Tylenol before bedtime and she said this sometimes lessens the severity of the episode, but does not eliminate it. Any ideas????