- Carbon monoxide poisoning or altitude sickness can be a cause of alarming sudden headaches. The headache is usually coupled with confusion and difficulties in breathing.
- Secondary headaches are sudden headaches caused by another illness such as glaucoma, epilepsy, meningitis, stroke, encephalitis or cancer.
- According to the Mayo Clinic in the article "Thunderclap Headaches," sudden intense headaches on one or both sides of the head can be caused by recent head injuries, pituitary gland problems or a brain aneurysm, which is a swollen blood vessel in the brain.
- Eating very cold food or drinking an icy drink can result in a sudden, intense "ice cream headache," but the pain lifts within 5 minutes. This type of headache is not life-threatening and is easily avoidable.
- According to Dianne Stafford and Jennifer Shoquist in their book, "Migraines For Dummies," anyone over age 50 who experiences her first sudden bad headache needs emergency medical attention.
