What could cause symptoms of seretonin syndrome?

The condition itself: Seretonin syndrome could cause symptoms of seretonin syndrome. Your question is sort of like asking what causes the symptoms of a hart attack. Well, a hart attack, for one. I encourage you to put some effort into rephrasing your question in such a way that you post the question you actually want answered.

Serotonin syndrome: Serotonin syndrome is a rare complication of SSRIs as Prozac, Zoloft, which increase the level of serotonin in the extracellular fluid.. Rarely, serotonin increases too much ( dosing or drug interactions) and there is hyperresponsiveness with agitation, fever, increased heart rate, muscle spasm which can lead to muscle breakdown. Stop the drug and give Xanax, (alprazolam) fluid. It is a medical emergency