Tension Headache: Often, tension headaches can worsen with certain positions due to increased muscle tension. Laying down can sometimes exacerbate this tension, especially if the sleeping position is not optimal.

Sinusitis: Sinus headaches can worsen when laying down due to increased pressure and congestion in the sinuses.
Migraine: While migraines can be triggered by various factors, some individuals may experience worsening symptoms when in a supine position, possibly due to increased intracranial pressure or other mechanisms.
Cervicogenic Headache: These headaches originate from the cervical spine and can be exacerbated by certain positions, including laying down, especially if there is an underlying cervical spine issue.

Subarachnoid Hemorrhage: Although less common, a sudden, severe headache that worsens with position changes, including laying down, could be indicative of a subarachnoid hemorrhage, which is a medical emergency.
Meningitis: Headaches due to meningitis can worsen with laying down and are often accompanied by fever, neck stiffness, and photophobia.
Increased Intracranial Pressure (ICP): Conditions leading to increased ICP, such as brain tumors or idiopathic intracranial hypertension, can cause headaches that worsen with laying down due to further increases in ICP in the supine position.

Chiari Malformation: A structural defect in the cerebellum that can cause headaches, especially with coughing, sneezing, or straining, and sometimes with position changes, including laying down.
Pseudotumor Cerebri: A condition characterized by increased intracranial pressure without a detectable cause, which can lead to headaches that may worsen in certain positions.
Arteriovenous Malformation (AVM): A rare condition where there is an abnormal connection between arteries and veins, which can cause headaches due to the risk of bleeding or increased pressure, potentially worsening with position changes.