Tension Headache: This is often exacerbated by stress and certain positions, including laying down, due to increased muscle tension in the neck and scalp.

Sinusitis: Laying down can increase pressure in the sinuses, leading to headache, especially if the patient has a pre-existing sinus infection.
Cervicogenic Headache: Arising from the cervical spine, these headaches can be triggered or worsened by certain positions, including laying down, due to mechanical stress on the cervical joints and muscles.
Migraine: While migraines can occur at any time, certain positions, including laying down, can sometimes trigger or exacerbate them, possibly due to changes in blood flow or pressure.

Subarachnoid Hemorrhage: Although rare, a sudden, severe headache that worsens with position changes, including laying down, could indicate a life-threatening condition like a subarachnoid hemorrhage.
Meningitis: Headache that worsens when laying down can be a symptom of meningitis, an infection of the protective membranes covering the brain and spinal cord, which requires immediate medical attention.
Brain Tumor: A headache that changes with position, including worsening when laying down, could be indicative of a brain tumor, especially if accompanied by other neurological symptoms.

Chiari Malformation: A structural defect in the cerebellum that controls balance can cause headaches that worsen with certain positions, including laying down, due to increased pressure on the brainstem.
Pseudotumor Cerebri (Idiopathic Intracranial Hypertension): Characterized by increased pressure within the skull without a detectable cause, symptoms can include headache that worsens with laying down, among other signs.
Arteriovenous Malformation (AVM): A rare condition where there's an abnormal connection between arteries and veins, which can cause headaches that may change with position due to altered blood flow dynamics.