Migraine: This condition is characterized by recurrent episodes of severe headaches, often accompanied by nausea, vomiting, and sensitivity to light and sound. The pressure behind the eye could be indicative of a migraine with aura, which includes neurological symptoms such as visual disturbances.

Sinusitis: Inflammation of the sinuses can cause pressure behind the eyes, headaches, and nausea. The dizziness could be related to the discomfort and pain associated with sinusitis.
Tension Headache: While typically less severe than migraines, tension headaches can cause significant discomfort, including pressure behind the eyes, and may be accompanied by nausea and dizziness.
Benign Paroxysmal Positional Vertigo (BPPV): This condition causes brief, intense episodes of vertigo triggered by specific head movements, which could be mistaken for dizziness. It might not directly cause nausea or pressure behind the eye but could contribute to the overall symptom complex.

Subarachnoid Hemorrhage: A life-threatening condition caused by bleeding into the space surrounding the brain, which can present with a sudden, severe headache (often described as "the worst headache" ever experienced), nausea, and potentially dizziness. The pressure behind the eye could be a sign of increased intracranial pressure.
Meningitis: Inflammation of the protective membranes covering the brain and spinal cord, which can cause headache, fever, nausea, and dizziness. The pressure behind the eye might be due to increased intracranial pressure or irritation of the cranial nerves.
Temporal Arteritis: Inflammation of the blood vessels in the temples, which can cause headaches, visual disturbances (including pressure behind the eyes), and systemic symptoms like nausea. It's a medical emergency due to the risk of blindness.

Acoustic Neuroma: A benign tumor on the nerve connecting the inner ear to the brain, which can cause dizziness, nausea, and pressure behind the eye due to its location and potential to compress adjacent structures.
Chiari Malformation: A structural defect in the cerebellum that controls balance, which can cause dizziness, headaches, and nausea, especially with certain head movements.
Pituitary Apoplexy: A condition caused by either a hemorrhage or an infarction of the pituitary gland, leading to sudden, severe headache, nausea, and potentially visual disturbances due to the gland's location near optic nerves.