Final answer:
To address sleep/wake cycle regulation issues and constant fatigue, a healthcare provider should check the patient's melatonin levels, which play a pivotal role in synchronizing circadian rhythms.
Step-by-step explanation:
If a patient is unable to regulate sleep/wake cycles and is constantly fatigued, the hormone level that should be checked is melatonin. Melatonin is primarily secreted by the pineal gland and plays a crucial role in regulating circadian rhythms, which determine our sleep-wake cycles. Higher levels of melatonin generally occur at night and promote sleep, while lower levels during the day aid in wakefulness. Melatonin release is influenced by light exposure to the eyes, signaling the brain's suprachiasmatic nucleus to modulate the secretion of melatonin based on the time of day. Disorders that affect melatonin secretion or its reception in the body can lead to sleep disruptions and chronic fatigue.
Additionally, it is worth noting that thyroid function can also affect sleep patterns and energy levels. The thyroid gland secretes hormones that regulate metabolism and can lead to fatigue when not properly balanced. However, given the specific complaint is related to sleep regulation, melatonin levels would be the most directly related hormone to assess initially.