Your body naturally produces serotonin that is needed for your brain and never cells to function properly but when your body gets too much serotonin it can cause symptoms such as mild shivering and diarrhea as well as severe muscle rigidity, fever and seizures.
If the high amounts of serotonin are not treated in time or properly then the high levels of serotonin can lead to severe serotonin syndrome which can be fatal.
If you think you have too much serotonin you need to seek medical attention or see your doctor and if it's an emergency either get to the emergency room or to urgent care soon.