Go to the emergency room for a headache that reaches its peak within seconds, a headache with fever and a stiff neck, or a headache with any neurological change such as weakness, trouble speaking or loss of vision.
Most headaches are not dangerous. A small number are, and they are recognizable. If any of the following applies, go to an emergency department or call 911 — do not wait for an appointment here.
Go now
- Thunderclap onset. A headache that reaches maximum intensity within seconds to a minute. The speed of onset is the warning sign, no matter how severe it ends up being.
- Headache with fever and a stiff neck, or with a new rash.
- Any neurological change — weakness, numbness, trouble speaking, loss of vision, double vision, unsteadiness, confusion, or a seizure.
- Headache after a head injury, particularly with vomiting, drowsiness or worsening.
- A new headache in someone who is pregnant or recently gave birth.
- A new or changed headache over the age of 50.
- A new headache in someone immunosuppressed or with a history of cancer.
- Headache with a red, painful eye and blurred vision.
- Headache that is consistently worse lying down, on waking, or with coughing and straining.
Why thunderclap is first on the list
Because the speed of onset is what sets it apart, and people routinely describe it by how severe it was instead. The question that matters is not “how bad was it” but “how long did it take to get that bad”. Seconds is the answer that requires emergency imaging.
If you have had a headache like that — even if it settled, even if it was weeks ago and you feel fine now — it should be assessed.
What we are, and what we are not
Headache Express is an outpatient clinic. We treat migraine, cluster and other recurring headache disorders, usually the same day. We do not have emergency imaging. We are not open overnight. We are not a substitute for an emergency department.
This line is the point of the clinic, not a limit on it. An emergency department is the right place for a headache that might be a bleed, an infection or a stroke. It is a poor place for a headache you already know the name of. You wait among sicker patients and often leave with a shot and a referral rather than a plan.
If you arrive here with features from the list above, we will tell you plainly and send you to an emergency department. That is the correct outcome, not a wasted visit.
What is not a red flag
Reassurance is worth as much as warning. So: severe pain by itself is not a red flag. Cluster headache is among the most severe pain in medicine and is not dangerous. Nausea and vomiting during a migraine are expected. Visual aura that builds over five to twenty minutes and clears within an hour is a recognized migraine feature.
What matters is change — a headache that is new, different from your usual pattern, or accompanied by something neurological that does not resolve.
If none of this applies
Then you are in the right place. See migraine treatment, cluster headache treatment, or the full list of treatments. Please contact us before coming in.
Common questions
My headache is the worst I’ve ever had, but it built over an hour. Is that thunderclap?
No. Thunderclap refers to onset within seconds. A severe headache that built over an hour is not thunderclap, though a new or unusually severe headache still deserves assessment. See contact us.
I had a sudden severe headache last month and I’m fine now. Do I still need to be checked?
Yes. A thunderclap headache that has settled still needs assessment. That is because some causes show up with a warning event before a larger one. That is an emergency department or urgent medical review, not an outpatient headache appointment. Once it has been ruled out, contact us about the ongoing headache pattern.
Is aura a warning sign?
Typical visual aura builds over 5 to 20 minutes and resolves within an hour. Sudden-onset visual loss, aura that does not resolve, or aura appearing for the first time over 50 are different and need assessment. See migraine treatment.
Should I go to the ER for a severe cluster attack?
Cluster pain is extreme but not dangerous. Emergency departments are often poorly set up to treat it. The better answer is a plan — including home high-flow oxygen — so you are not dependent on an ER at 3am.
If none of the red flags on this page apply, a bad headache rarely needs the ER, and office care the same day is faster. That is what our headache clinic in St. Louis is for; anything on the red-flag list still goes to the emergency room first.
Separately from the emergency question, it is worth knowing which headaches warrant a scan at all and which do not — see when a headache actually needs a scan.
Sources
- Do TP, Remmers A, Schytz HW, et al. Red and orange flags for secondary headaches in clinical practice: SNNOOP10 list. Neurology, 2018. PMID 30587518. pubmed.ncbi.nlm.nih.gov
- Sjulstad AS, Brekke OL, Odeh F, et al. Incidence and outcome of sudden severe headache in the emergency department. Headache, 2025. PMID 40859708. pubmed.ncbi.nlm.nih.gov