Tension Headache: This is the most common type of headache and often presents with pain behind the eyes, typically described as a band or a squeezing sensation around the forehead. The pain is usually mild to moderate, bilateral, and can be associated with stress or muscle tension.

Migraine: Migraines can cause severe, unilateral pain that may be localized behind one eye. They are often accompanied by other symptoms such as nausea, vomiting, sensitivity to light and sound, and sometimes visual auras.
Sinusitis: Inflammation of the sinuses can cause pain behind the eyes, especially if the ethmoid or frontal sinuses are involved. This pain is often accompanied by nasal congestion, facial pressure, and sometimes fever.
Cluster Headache: These are extremely painful headaches that occur in cycles or clusters, often waking the patient from sleep. The pain is typically unilateral and centered around one eye, with associated symptoms like nasal congestion, rhinorrhea, and ptosis on the affected side.

Giant Cell Arteritis: This condition involves inflammation of the blood vessels and can cause severe headaches, often localized to one side of the head or behind the eyes. It's crucial to diagnose promptly because it can lead to blindness if not treated. Risk factors include age over 50 and symptoms like jaw claudication or visual disturbances.
Temporal Arteritis: Similar to giant cell arteritis, temporal arteritis can cause headaches behind the eyes due to inflammation of the temporal artery. It's essential to consider this diagnosis in older adults, especially those with systemic symptoms like fever or weight loss.
Pituitary Apoplexy: A medical emergency where the pituitary gland suddenly hemorrhages or becomes infarcted, leading to severe headache, often behind the eyes, along with visual disturbances, nausea, and altered mental status.
Subarachnoid Hemorrhage: Although the headache is typically described as "the worst headache of my life" and is often diffuse, it can sometimes be localized behind the eyes. It's associated with sudden onset, possible loss of consciousness, and sometimes neck stiffness.

Trigeminal Neuralgia: A chronic pain condition that affects the trigeminal nerve, which can cause intense shock-like or stabbing pain in parts of the face, including behind the eyes. However, the pain is usually more superficial and localized to one side of the face.
Idiopathic Intracranial Hypertension (IIH): Also known as pseudotumor cerebri, this condition involves increased pressure within the skull without any apparent cause. Symptoms can include headache that worsens with coughing or straining, vision changes, and tinnitus. The headache can be diffuse but may also be perceived behind the eyes.
Cavernous Sinus Thrombosis: A rare but serious condition involving a blood clot in the cavernous sinus, which can cause headache behind the eyes, along with symptoms like fever, ptosis, and ophthalmoplegia.