Serotonin syndrome symptoms usually occur within several hours of taking a new drug or increasing the dose of a drug you're already taking. Signs and symptoms include: 
Agitation or restlessness
Insomnia
Confusion
Rapid heart rate and high blood pressure
Dilated pupils
Loss of muscle coordination or twitching muscles
High blood pressure
Muscle rigidity
Heavy sweating
Diarrhea
Headache
Shivering
Goose bumps
 Severe serotonin syndrome can be life-threatening. Signs include: 
High fever
Tremor
Seizures
Irregular heartbeat
Unconsciousness
