Flu symptoms often feel more pronounced at night. This is due to a combination of the body’s natural biological rhythms and the physical effects of resting.
The Influence of Your Body’s Internal Clock
The body operates on an internal 24-hour cycle known as the circadian rhythm, which influences various physiological processes, including the immune system’s activity. Immune cells, such as macrophages and lymphocytes, exhibit rhythmic functions, with their numbers and effectiveness varying throughout the day. This internal clock helps regulate when the immune system is more active in fighting off pathogens.
During sleep, the immune system often becomes more active in its fight against infection. This heightened activity involves the release of inflammatory chemicals, which can intensify symptoms like fever, aches, and congestion. Levels of the hormone cortisol, which typically suppresses inflammation, naturally decrease during the evening and night. As cortisol levels drop, the immune response can increase, leading to a more noticeable inflammatory reaction.
Conversely, melatonin, a hormone that promotes sleep and has immune-enhancing properties, rises at night. The interplay between decreasing cortisol and increasing melatonin contributes to the immune system’s nocturnal peak in activity. This shift can cause flu symptoms to feel more severe.
How Gravity Affects Respiratory Symptoms
During the day, when a person is upright, gravity assists in draining mucus from the nasal passages and throat. This natural drainage helps prevent mucus accumulation and clears airways. However, when lying down, this gravitational assistance is lost, and mucus can begin to pool in the back of the throat and sinuses.
This pooling of mucus can lead to increased congestion and post-nasal drip. Post-nasal drip can irritate the throat, causing a persistent tickle and a heightened urge to cough. The combination of blocked nasal passages and throat irritation often makes breathing more difficult and coughing spells more frequent and intense at night. Elevating the head with pillows can sometimes help facilitate drainage and reduce these respiratory symptoms.
The Role of Medication Timing
Many over-the-counter and some prescription medications used for flu symptom relief have a limited duration of action. Pain relievers and fever reducers, for instance, often provide relief for about 4 to 8 hours. Cough suppressants, antihistamines, and oral decongestants also have specific timeframes for their effectiveness.
If a dose is taken during the day, its effects may wear off significantly by the middle of the night. As the medication’s alleviating properties diminish, symptoms can resurface with full intensity. This timing issue means that without active medication, the discomfort from fever, congestion, and coughing can become more noticeable during periods of rest.