Coffee poisoning, or caffeine overdose, can cause a range of symptoms, including:
Mild symptoms:
Headache, nausea, vomiting, anxiety, insomnia, dizziness, or irritability
Severe symptoms:
Convulsions (seizures), rapid heartbeat, irregular heartbeat, breathing trouble, agitation, confusion, hallucinations, diarrhea, fever, increased thirst, increased urination, and muscle twitching
Complications:
Neurologic changes, tachy-dysrhythmia, ECG changes, hypokalemia, hyperglycemia, acute kidney injury, rhabdomyolysis, and cardiac arrest