Participants will spend 4 days/3 nights in the laboratory to uncover circadian rhythms. After 2 nights for acclimatization and baseline measurements, participants will stay awake for 28 hours in dim light, constant temperature, and semi-recumbent posture. Participants will be provided with standardized snacks regularly. Polysomnography, core body temperature, sleep, finger oximetry, electrocardiogram (ECG), and beat-to-beat BP will (except microneurography) be measured throughout. Blood will be drawn every 2-4h to analyze catecholamines, renin activity, and aldosterone. All other measurements, including BP, heart rate (HR), and flow-mediated dilation will be performed regularly. Salivary samples will be collected every 2hrs (when awake) to analyze melatonin levels. A recovery sleep period will be provided and baseline testing procedures will be performed. Investigators may acquire direct recordings of sympathetic activity using microneurography.

Participants will start wearing an ambulatory BP monitor upon admission. Participants will be instrumented with full polysomnography (except leg myogram), and an intravenous catheter will be placed in the non-dominant arm. Participants will receive a standardized snack, and dinner ~4 hours before the start of the trial. Participants will be instrumented for microneurography. Participants will be awake in bed in dim light (<8 lux). An investigator will constantly be present in the control room to monitor and ensure constant supine posture and wakefulness. Polysomnography, beat-by-beat BP, and neurogram for microneurography will be done throughout each trial into awakening; blood will be sampled before, during, and immediately after each trial (total of 8 samples in each trial). Flow-mediated dilation will be conducted before bed and after bed. The two trials will be conducted ~one month apart to accommodate the menstrual cycle phase in pre-menopausal females.

Participants will wear an ambulatory BP monitor upon admission. Participants will be instrumented with full polysomnography (except leg myogram), and an intravenous catheter will be placed in the non-dominant arm, and then participants will receive a standardized snack, and dinner 4 hours before the start of the trial. Polysomnography, beat-by-beat BP, and neurogram for microneurography will be done throughout each trial into awakening; blood will be sampled before, during, and immediately after each trial (total of 8 samples in each trial). Participants will be instrumented for microneurography. Participants will begin an 8-hour sleep opportunity (<0.1 lux) at their chosen sleep time. At the end of the sleep episode, participants will be gently awoken in a standardized fashion by use of a mild auditory stimulus. Flow-mediated dilation will be conducted before bed and after sleep. The two trials will be conducted one month apart to accommodate the menstrual cycle.

All participants will be asked to maintain a self-selected bedtime (sleep duration not controlled) for two weeks as an intervention after the completion of the constant routine and both the resting wakefulness and overnight sleep trials. During this time, participants will be asked to call a time-stamped voicemail box upon waking and going to bed, as well as complete a daily sleep diary and wear an Actigraph device on their wrist. Ambulatory blood pressure will be measured at home before and at the end of the two-week intervention.

Plasma epinephrine (measured in plasma according to laboratory values) will be measured to estimate sympathetic output (stress). Higher values may indicate increased cardiovascular risk. Investigators will study circadian rhythms in Epinephrine between people with dipping vs non-dipping hypertension. Investigators will also study how overnight sleep affects Epinephrine in these groups.

Plasma norepinephrine (measured in plasma according to laboratory values) will be measured to estimate sympathetic output (stress). Higher values may indicate increased cardiovascular risk. Investigators will study circadian rhythms in Norepinephrine between people with dipping vs non-dipping hypertension. Investigators will also study how overnight sleep affects Norepinephrine in these groups.

Plasma aldosterone (measured in plasma according to laboratory values) will be measured to estimate sympathetic output (stress). Higher values may indicate increased cardiovascular risk. Investigators will study circadian rhythms in Aldosterone between people with dipping vs non-dipping hypertension. Investigators will also study how overnight sleep affects Aldosterone in these groups.

Plasma renin/activity (measured in plasma according to laboratory values) will be measured to estimate sympathetic output (stress). Higher values may indicate increased cardiovascular risk. Investigators will also study circadian rhythms in renin between people with dipping vs non-dipping hypertension. Investigators will also study how overnight sleep affects renin in these groups.

Investigators will measure endothelial function as flow-mediated dilation (FMD). Investigators will measure brachial artery FMD using standard procedures every 3 hours in the constant routine protocol and while awake during the overnight sleep vs. rested wakefulness trial. Investigators will also normalize FMD to the hyperemic shear. Investigators will study circadian rhythms in vascular function in people with dipping vs non-dipping hypertension. Investigators will also study if overnight sleep changes morning vascular function between these groups. Vascular function may be an indicator of cardiovascular health.

Blood Pressure (BP) dipping will be calculated as the percent reduction in average nighttime BP reduction compared to daytime BP. Both systolic and diastolic blood pressure will be measured in mmHg. Blood pressure dipping status may be an indicator of cardiovascular health. Investigators will study whether being asleep or not changes the magnitude of dipping between dipping and non-dipping hypertension. Investigators will also measure ancillary variables such as average daytime BP, night time BP, and morning surge in BP.

MSNA may be directly measured by inserting a tungsten microelectrode (Frederick Haer, Bowdoinham, ME) into a peroneal nerve at the popliteal fossa. A reference electrode will be inserted subcutaneously 2-3 cm from the recording electrode. Both electrodes will be connected to a differential preamplifier and then to an amplifier to obtain mean voltage neurograms. Once investigators have confirmed a satisfactory post-ganglionic MSNA recording, the participants will be provided a 10 min non-recorded rest to ensure baseline levels. Data will be recorded using WinDaq/Pro data acquisition software (DATAQ Instruments, Akron, OH) and imported for analysis in the commercially available WinCPRS software program (Absolute Aliens; Turku, Finland). Investigators will also study how overnight sleep affects MSNA in these groups. Investigators may also study circadian rhythms in MSNA between people with dipping vs non-dipping hypertension.

Participants will be instructed to select a preferred bedtime time and ensure adherence to that time for 2-weeks. Investigators will not control sleep duration. Both systolic and diastolic blood pressure will be measured in mmHg. Blood pressure dipping status will be assessed. BP dipping will be calculated as the percent reduction in average nighttime BP reduction compared to daytime BP. Blood pressure dipping status may be an indicator of cardiovascular health.