Tension headache: This is the most common type of headache and can last from 30 minutes to several days, making it a likely candidate for a headache lasting 5 days. The pain is usually described as a band or a squeezing sensation around the forehead, back of the neck, or both.

Migraine: Migraines can last anywhere from 4 to 72 hours but can also have a prolonged or subacute course, making them a possible cause for a 5-day headache. They are often accompanied by other symptoms such as nausea, vomiting, and sensitivity to light and sound.
Cluster headache: Although cluster headaches are typically shorter, lasting 15 minutes to 3 hours, they can occur in clusters or cycles that might persist for days, potentially explaining a headache lasting 5 days. They are characterized by severe, one-sided pain, often around the eye.
Sinus headache: Inflammation or infection of the sinuses can cause headaches that last for several days. The pain is usually localized to the face and forehead and can be accompanied by other symptoms such as nasal congestion and fever.

Subarachnoid hemorrhage: Although typically presenting with a sudden, severe headache (often described as "the worst headache of my life"), in some cases, the onset can be more gradual, and the headache can persist. It's crucial to consider this diagnosis due to its high morbidity and mortality.
Meningitis: Inflammation of the protective membranes covering the brain and spinal cord can cause a severe headache that lasts for days, along with fever, stiff neck, and confusion. Early diagnosis is critical for effective treatment.
Temporal arteritis: This condition, characterized by inflammation of the blood vessels in the head, can cause persistent headaches, often accompanied by jaw claudication and visual disturbances. It's a medical emergency due to the risk of blindness if not promptly treated.

Brain tumor: Although rare, a brain tumor can cause persistent headaches that worsen over time. The headaches can be accompanied by other neurological symptoms such as seizures, confusion, and focal neurological deficits.
Idiopathic intracranial hypertension (IIH): This condition, characterized by increased pressure within the skull without any apparent cause, can lead to persistent headaches, often accompanied by visual disturbances and tinnitus.
Trigeminal neuralgia: This condition involves sudden, severe, shock-like pain around the eyes, lips, or nose mainly because of abnormal blood vessels pressing on the trigeminal nerve in the head. While the pain episodes are typically brief, they can recur frequently over days.