The main symptom is a severe headache that starts suddenly and is often worse near the back of the head. Patients often describe it as the "worst headache ever" and unlike any other type of headache pain. The headache may start after a popping or snapping feeling in the head.

Other symptoms:

• Sudden or decreased consciousness and alertness
• Difficulty or loss of movement or feeling
• Mood and personality changes, including confusion and irritability
• Muscle aches (especially neck pain and shoulder pain)
• Nausea and vomiting
• Photophobia (light bothers or hurts the eyes)
• Seizure
• Stiff neck
• Vision problems, including double vision, blind spots, or temporary vision loss in one eye

Additional symptoms that may be associated with this disease:

• Eyelid drooping
• Eyes, pupils different size
• Sudden stiffening of back and neck, with arching of the back (Opisthotonos; not very common)
• Seizures

A physical exam may show a stiff neck due to irritation by blood of the meninges, the tissues that cover the brain. Except those in a deep coma, persons with a subarachnoid hemorrhage may resist neck movement.

A neurological exam may show signs of decreased nerve and brain function (focal neurologic deficit).

An eye exam will be performed. Decreased eye movements can be a sign of damage to the cranial nerves. In milder cases, no problems may be seen on an eye exam.

If your doctor thinks you may have a subarachnoid hemorrhage, a head CT scan (without dye contrast) should be immediately done. In some cases, the scan may be normal, especially if there has only been a small bleed. If the CT scan is normal, a lumbar puncture (spinal tap) must be performed. Patients with SAH will have blood in their spinal fluid.

CT scan angiography (using contrast dye) may be done to look for evidence of and aneurism.

Cerebral angiography of blood vessels of the brain is better than CT angiography to show small aneurysms or other vascular problems. This test can pinpoint the exact location of the bleed and can tell if there are blood vessel spasms.

Transcranial doppler ultrasound is used to look at blood flow in the arteries of the brain that run inside the skull. The ultrasound beam is directed through the skull. It can also detect blood vessel spasms and may be used to guide treatment.

Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) are occasionally used to diagnose a subarachnoid hemorrhage or find other associated conditions.