When your body is in danger, it will warn you in advance:

Acute conditions: Chest pain + sweating (myocardial infarction)
Acute conditions: Headache + vomiting (intracranial hemorrhage)
Acute conditions: Difficulty breathing + cyanosis (acute respiratory failure)
Cerebrovascular: Sudden slurred speech (stroke)
Cerebrovascular: Numbness in one side of body (transient ischemic attack)
Cerebrovascular: Mouth corner deviation (stroke)
Cerebrovascular: Sudden severe headache (subarachnoid hemorrhage)
Cerebrovascular: Sudden loss of balance (cerebellar infarction)
Cerebrovascular: Transient blindness (retinal artery occlusion)
Cerebrovascular: Recurrent dizziness (vertebrobasilar insufficiency)
Cardiovascular: Chest pressure (coronary artery disease)
Cardiovascular: Chest pain radiating to left arm (myocardial infarction)
Cardiovascular: Shortness of breath after activity (heart failure)
Cardiovascular: Awakening breathless at night (heart failure)
Cardiovascular: Irregular heartbeat (arrhythmia)
Cardiovascular: Bilateral leg edema (right heart failure)
Cardiovascular: Fainting (ventricular arrhythmia)
Respiratory system: Bluish lips (cyanosis)
Respiratory system: Persistent cough (lung cancer)
Respiratory system: Coughing up blood (tuberculosis)
Respiratory system: Chest pain with difficulty breathing (pulmonary embolism)
Respiratory system: Nighttime cough (bronchial asthma)
Digestive: Difficulty swallowing (esophageal cancer)
Digestive: Black stools (gastrointestinal bleeding)
Digestive: Chronic stomach pain (gastric cancer)
Digestive: Decreased appetite (liver cancer)
Digestive: Abdominal mass (pancreatic cancer)
Digestive: Abdominal bloating after meals (chronic gastritis)
Metabolic: Excessive drinking and urination (diabetes)
Metabolic: Darkened neck (insulin resistance)
Metabolic: Sudden obesity (hypothyroidism)
Metabolic: Heat intolerance and palpitations (hyperthyroidism)
Systemic: Unexplained weight loss (malignant tumor)
Systemic: Persistent low-grade fever (lymphoma)
Systemic: Night sweats (tuberculosis)
Neurological: Hand tremor (Parkinson's disease)
Neurological: Decreased memory (Alzheimer's disease)
Neurological: Facial twitching (hemifacial spasm)
Urinary: Blood in urine (bladder cancer)
Urinary: Difficulty urinating (benign prostatic hyperplasia)
Urinary: Foamy urine (nephrotic syndrome)
Male: Loss of morning erections (atherosclerosis)
Male: Testicular lump (testicular cancer)
Female: Abnormal vaginal bleeding (cervical cancer)
Female: Breast lump (breast cancer)