Abstract: Preclinical and clinical studies have shown that the autonomic nervous system (parasympathetic and sympathetic nervous systems) show reliable changes across the sleep wake cycle. Most importantly, the parasympathetic nervous system shows increased activity during sleep consistent with its role in regulating rest. Further, patients with insomnia show reduced parasympathetic activity and/or increased sympathetic activity during sleep consistent with a neurobiological model of “hyperarousal”. Described herein are methods and apparatuses that activate the parasympathetic nervous system in response to a diving reflex; a sustained diving reflex may, surprisingly, lead to enhancing sleep. The apparatuses and methods described herein may specifically and/or selectively activate this reflex may play a therapeutic role in the modulation of sleep in insomnia patients.