It is common to feel more unwell at night and in the morning. This is due to distinct biological and environmental factors that worsen illness symptoms during these periods. The human body undergoes various changes throughout a 24-hour cycle, impacting how it responds to illness. Understanding these causes explains why symptoms often intensify during rest or upon waking.
The Body’s Internal Clock and Immune Response
The body operates on an internal 24-hour cycle known as the circadian rhythm, which influences many bodily functions, including the immune system. This biological clock, controlled by the suprachiasmatic nucleus (SCN) in the brain, synchronizes with environmental cues like light and temperature. The circadian rhythm affects immune cell activity and inflammatory responses, leading to fluctuations in how the body fights infections.
Immune cells often show peak activity at night, indicating a heightened immune response. This nocturnal surge in immune function, particularly phagocytosis (where immune cells engulf pathogens), suggests the body is “on alert” to combat threats or repair itself during rest. This redirection of energy towards immune functions during sleep can lead to more pronounced symptoms as the immune system actively engages with pathogens.
Hormonal Shifts During Sleep
Hormones modulate the immune system and influence how one feels sick. Cortisol, a steroid hormone, follows a natural circadian rhythm, peaking in the early morning and declining throughout the day. Cortisol has immunosuppressive and anti-inflammatory effects, influencing the body’s inflammatory response.
As cortisol levels dip at night, its anti-inflammatory effects are reduced, allowing inflammatory responses to become more noticeable. The rise in cortisol in the morning can temporarily worsen inflammation before symptoms improve. Melatonin, produced in darkness, supports immune function by enhancing certain immune cells and possesses antioxidant properties, further modulating the immune system at night.
Physiological Effects of Lying Down and Sleep
Lying down during sleep can exacerbate illness symptoms. When upright, gravity helps drain mucus from the nasal passages and throat. Lying flat allows mucus to pool, leading to increased congestion, post-nasal drip, and a persistent cough, which often worsens at night.
Acid reflux, where stomach acid flows back into the esophagus, can also become more prevalent when lying down. This irritates the throat, leading to a sore throat, hoarseness, and a chronic cough. Additionally, natural dehydration overnight can thicken mucus, making it harder to clear and worsening respiratory symptoms upon waking. These changes contribute to feeling sicker at night and in the morning.
Environmental Triggers and Morning Exposure
The sleep environment can house various environmental triggers that worsen symptoms. Bedrooms often contain a higher concentration of allergens like dust mites, pet dander, and mold spores. Dust mites thrive in bedding and can trigger allergic reactions such as sneezing, congestion, and itchy eyes.
Pollen can transfer from hair, skin, and clothing to bedding, increasing exposure during sleep. These prolonged exposures can trigger inflammatory responses or allergic reactions that intensify overnight and are most noticeable upon waking. Dry air from heating or cooling systems can also irritate respiratory passages, contributing to congestion and a sore throat upon rising.