Emergency warning signs, by body system.

Heart and circulation

• Chest pain, pressure, tightness, squeezing — especially radiating to arm, jaw, neck, back, or stomach.
• Sudden severe shortness of breath, particularly with chest discomfort or sweating.
• Fainting, near-fainting, or unexplained collapse.
• New irregular heartbeat with dizziness or chest discomfort.
• One leg suddenly swollen, painful, and warm — possible blood clot.

Brain and nervous system

Use the FAST rule:

• Face drooping on one side.
• Arm weakness or numbness, often on one side.
• Speech slurred, garbled, or hard to find words.
• Time — note when symptoms started and call 911 immediately.

Other neurological red flags:

• Sudden, severe headache unlike any before — "thunderclap" onset.
• New confusion, difficulty staying awake, or unusual personality change.
• Seizure, especially a first-ever seizure or one in pregnancy.
• Sudden vision loss, double vision, or severe vertigo.
• Sudden severe weakness or numbness, especially one-sided.

Breathing

• Trouble breathing at rest, or unable to speak in full sentences.
• Blue lips, blue fingertips, or pale-gray skin tone.
• Severe wheezing, stridor (high-pitched breathing), or sense of throat closing.
• Coughing up blood.
• Chest pain with breathing — especially if it started suddenly or after a long flight, surgery, or period of immobility.

Severe allergic reactions (anaphylaxis)

• Throat tightness, difficulty swallowing, hoarse voice.
• Lip, tongue, or face swelling.
• Hives or widespread rash with breathing trouble or dizziness.
• Sudden vomiting plus rash plus weakness after a known allergen.

If an epinephrine auto-injector is available, use it and call 911 — even if symptoms seem to ease afterward.

Bleeding and trauma

• Bleeding that does not slow with firm direct pressure for 10 minutes.
• Vomiting blood, or vomit that looks like coffee grounds.
• Black, tarry, or bright-red stools.
• Significant head injury, especially with vomiting, confusion, or loss of consciousness.
• Possible broken bone with deformity, severe pain, or numbness.
• Deep wound, animal bite, or burn larger than the palm or affecting face/hands/joints.

Abdominal symptoms

• Severe abdominal pain — especially in the lower right or upper right side.
• Pain plus fever, plus vomiting, plus inability to keep fluids down.
• Sudden, severe pain in someone who recently had abdominal surgery.
• Rigid, board-like abdomen.
• Signs of dehydration: very little urination, dark urine, dizziness on standing.

Pregnancy

• Heavy vaginal bleeding or passing tissue.
• Severe abdominal or pelvic pain.
• Severe headache, vision changes, or sudden swelling — possible preeclampsia.
• Decreased or absent fetal movement past viability.
• Leaking fluid, regular contractions before 37 weeks.
• Fever ≥100.4°F (38°C) at any point in pregnancy.

Infants and young children

• Any rectal temperature ≥100.4°F (38°C) in an infant under 3 months.
• Lethargy — hard to wake, not engaging, very limp.
• Rapid breathing, ribs visibly pulling in with each breath, or bluish color.
• Persistent inability to keep down fluids, or no wet diaper for 8+ hours.
• Stiff neck, bulging soft spot, or rash that doesn't fade when pressed.
• Seizure, especially first-ever.

Mental health emergencies

• Suicidal thoughts with a plan, or active intent to harm yourself or others.
• Severe psychotic symptoms or sudden inability to function safely.

In the U.S., dial or text 988 for the Suicide & Crisis Lifeline. Call 911 if there is immediate danger. Outside the U.S., contact your local crisis line or emergency number.

Possible poisoning, overdose, or environmental

• Suspected overdose, accidental ingestion, or unknown chemical exposure.
• Carbon monoxide concern: headache, dizziness, nausea in multiple people in the same building.
• Heat stroke: hot, dry skin, confusion, very high body temperature.
• Severe hypothermia: shivering stopped, confusion, slurred speech, slow breathing.

In the U.S., the Poison Control hotline is 1-800-222-1222. Call 911 if the person is unresponsive or having trouble breathing.

Educational reference only. See Medical Disclaimer. Related: When to Seek Urgent Care · Symptom Hub · Family Preparedness.