Activity in her limbic system's "hypothalamus" probably contributes to this experience.
The limbic system is the segment of the cerebrum that deals with three key capacities: feelings, memories and excitement. The ventrolateral preoptic nucleus of the hypothalamus is one territory of the mind that is especially associated with the switch among attentiveness and sleep. Neurons in this little zone help to advance sleep by hindering movement in regions of the brainstem that look after attentiveness.