Any doctor will tell you most health emergencies happen at night. Most heart attacks occur in the early hours of the morning. They are linked to the platelets in the blood becoming stickier and more prone to clotting at night.

Patients with acute heart failure start coming to the hospitals around 3 am. When the heart can no longer pump out enough of the blood it receives from the lungs, fluid builds up in the chest, known as acute heart failure.

Chronic obstructive pulmonary disease describes a collection of conditions causing lung damage, including chronic bronchitis and emphysema, causing inflammation in the lungs, often along with permanent damage to the airways. Studies have found less air passes through lungs during sleep. The body also responds less efficiently to increasing carbon dioxide levels in the blood during sleep, so breathing rates do not rise in the same way as during the day to expel it from the body. Excess carbon dioxide eventually causes someone to wake up, often gasping for breath.

Colds get worst at night. The lining of the airways constantly carries debris and fluid out of the lungs into the throat. This process becomes less effective at night because we are horizontal, causing congestion and coughing.

Arthritis, sciatica, chronic back pain cause painful inflammation in cartilage and bone in the joints. Being inactive for a long period of time while asleep will make pain worst. The probable cause – joint linings become congested with excess fluid used to bathe cells, and protein waste products when joints are immobile for a length of time.

Research shows that our bodies are on a 24-hour clock called a circadian rhythm. Hormone levels fluctuate within this daily cycle. Cortisol, a hormone made by the adrenal glands, helps regulate blood sugar levels, metabolism, and blood pressure. It helps the body manage stress.

There is less cortisol in our blood at night. The white blood cells readily detect and fight infections, provoking the symptoms of the infection to surface, such as fever, congestion, chills, or sweating. Thus, we feel sicker at night.