A system configured to manage a current sleep session of a subject, the system comprising: one or more sensory stimulators configured to provide sensory stimuli to the subject; one or more sensors configured to generate output signals conveying information related to a blood volume of the subject during the current sleep session, the one or more sensors include an optical sensor configured to be carried by an extremity of the subject, the optical sensor including a light source configured to light an area of skin on the extremity of the subject, wherein at least some of the light is absorbed by blood in blood vessels of the area of skin; and a photodiode assembly configured to generate output signals indicating an amount of light from the light source not absorbed by the blood in the blood vessels in the area of skin, the amount of light not absorbed being related to the blood volume of the blood vessels in the area of skin; and one or more processors configured to execute computer program modules, the computer program modules comprising: a parameter module configured to determine a blood volume metric, the blood volume metric being related to a current sleep stage of the subject during the current sleep session; a sleep stage module configured to determine the current sleep stage of the subject based on the determined blood volume metric, the sleep stage module configured to determine whether the subject is presently in slow wave sleep based at least in part on differences in the intensities of low frequency oscillations of the blood volume in a range of 0.04-0.3 Hz; and a control module configured to control the one or more sensory stimulators to provide the sensory stimuli to enhance slow wave activity in the subject while the subject is determined to be in slow wave sleep. one or more sensory stimulators configured to provide sensory stimuli to the subject; one or more sensors configured to generate output signals conveying information related to a blood volume of the subject during the current sleep session, the one or more sensors include an optical sensor configured to be carried by an extremity of the subject, the optical sensor including a light source configured to light an area of skin on the extremity of the subject, wherein at least some of the light is absorbed by blood in blood vessels of the area of skin; and a photodiode assembly configured to generate output signals indicating an amount of light from the light source not absorbed by the blood in the blood vessels in the area of skin, the amount of light not absorbed being related to the blood volume of the blood vessels in the area of skin; and one or more processors configured to execute computer program modules, the computer program modules comprising: a parameter module configured to determine a blood volume metric, the blood volume metric being related to a current sleep stage of the subject during the current sleep session; a sleep stage module configured to determine the current sleep stage of the subject based on the determined blood volume metric, the sleep stage module configured to determine whether the subject is presently in slow wave sleep based at least in part on differences in the intensities of low frequency oscillations of the blood volume in a range of 0.04-0.3 Hz; and a control module configured to control the one or more sensory stimulators to provide the sensory stimuli to enhance slow wave activity in the subject while the subject is determined to be in slow wave sleep. a parameter module configured to determine a blood volume metric, the blood volume metric being related to a current sleep stage of the subject during the current sleep session; a sleep stage module configured to determine the current sleep stage of the subject based on the determined blood volume metric, the sleep stage module configured to determine whether the subject is presently in slow wave sleep based at least in part on differences in the intensities of low frequency oscillations of the blood volume in a range of 0.04-0.3 Hz; and a control module configured to control the one or more sensory stimulators to provide the sensory stimuli to enhance slow wave activity in the subject while the subject is determined to be in slow wave sleep.