Tension Headache: This is the most common type of headache and is often associated with fatigue, stress, and muscle tension. The duration of 5 days is consistent with a prolonged tension headache.

Migraine: Although typically more severe and often accompanied by other symptoms like nausea, vomiting, and sensitivity to light and sound, migraines can present with fatigue and may last for several days.
Viral Infection: Such as a common cold or flu, which can cause headache and fatigue due to the body's immune response.
Dehydration: Inadequate fluid intake can lead to headaches and fatigue, and this condition is relatively common and easily treatable.
Sleep Disorder: Issues like insomnia or sleep apnea can cause both headache and fatigue due to poor sleep quality.

Subarachnoid Hemorrhage: Although less likely, this condition is life-threatening and requires immediate medical attention. It typically presents with a sudden, severe headache but can have a more gradual onset in some cases.
Meningitis: Infection of the meninges can cause headache, fatigue, fever, and stiff neck. It's crucial to identify and treat promptly to prevent serious complications.
Temporal Arteritis: This condition, more common in older adults, involves inflammation of the blood vessels and can cause headache, fatigue, and visual disturbances. If untreated, it can lead to blindness.
Brain Tumor: Although rare, a brain tumor can cause headache and fatigue among other symptoms, and early detection is critical for treatment.

Chronic Daily Headache: A condition characterized by headaches that occur 15 days or more per month, which could be a consideration if the headache persists beyond the initial 5 days.
Hypothyroidism: Fatigue and headache can be symptoms of an underactive thyroid gland, though this would typically be accompanied by other signs such as weight gain and cold intolerance.
Anemia: Low red blood cell count or hemoglobin can cause fatigue and sometimes headache, usually accompanied by other symptoms like pale skin and shortness of breath.
Lupus: Systemic lupus erythematosus is an autoimmune disease that can cause a wide range of symptoms, including headache and fatigue, but is relatively rare and typically involves other systemic symptoms.