Nocturnal Leg Cramps: This condition is characterized by sudden, severe muscle cramps in the legs, typically occurring at night. The pain is often localized to the calf muscles and can be severe enough to wake the patient from sleep. The exact cause is often unknown, but it can be related to muscle fatigue, dehydration, or electrolyte imbalances.

Peripheral Artery Disease (PAD): PAD can cause intermittent claudication, which is pain in the legs or buttocks during exercise that is relieved by rest. However, in some cases, the pain can occur at rest, especially at night, and is known as rest pain. This condition is more common in smokers and those with diabetes or high blood pressure.
Varicose Veins: While varicose veins can cause discomfort and aching in the legs during the day, the symptoms can worsen at night due to increased venous pressure when lying down.
Muscle Strain or Overuse: Individuals who engage in strenuous physical activity, especially those involving running or jumping, can experience muscle strain or overuse injuries that lead to pain in the legs and calves, potentially worsening at night due to increased muscle spasms.

Deep Vein Thrombosis (DVT): DVT is a blood clot that forms in the deep veins of the body, often in the legs. It can cause pain, swelling, and warmth in the affected leg. While DVT can occur at any time, nocturnal worsening of pain could be a symptom, and missing this diagnosis can lead to potentially fatal pulmonary embolism.
Compartment Syndrome: This is a condition where pressure within the muscles builds to dangerous levels, decreasing blood flow and potentially leading to nerve and muscle damage. It can cause severe pain, especially at night, and is a medical emergency.

Neurological Conditions: Certain neurological conditions, such as peripheral neuropathy or radiculopathy, can cause pain in the legs that worsens at night. These conditions can result from various causes, including diabetes, vitamin deficiencies, or nerve root compression.
Osteomyelitis or Bone Infections: Infections of the bone can cause severe pain that worsens at night. These conditions are less common but can be serious and require prompt medical attention.
Erythromelalgia: A rare disorder characterized by burning pain, heat, and redness in the hands and feet, which can worsen at night. It can be primary (idiopathic) or secondary to other conditions like myeloproliferative disorders.