A subarachnoid hemorrhage is bleeding in the space between the brain and the surrounding membrane (subarachnoid space). The primary symptom is a sudden, severe headache. Some people describe it as the worst headache they have ever felt. Along with having a headache, some people may experience:

  • Nausea
  • Vomiting
  • Stiff neck
  • Problems with vision
  • Brief loss of consciousness

Bleeding usually happens when an irregular bulge in a blood vessel (aneurysm) bursts in the brain. Sometimes, bleeding is caused by trauma, a tangle of blood vessels in the brain (arteriovenous malformation), or other blood vessel or health problems.

Untreated, a subarachnoid hemorrhage can lead to permanent brain damage or death.