There are several symptoms that usually happen when one overdoses on caffeine. The first to be experienced include feeling restless, nervous, and just generally jittery. Heartbeat will start to rise, and you might feel nauseous and anxious. Things start to get really serious when heart palpitations or cardiac arrhythmia sets in, you lose total focus and can’t sleep, start to sweat and feel dizzy. You might actually end up vomiting, and in very extreme cases, you could go into cardiac arrest.