Is it possible to die of serotonin syndrome?

Yes, if severe: Severity of serotonin syndrome can very from mild to fatal. If significant symptoms are present, that can constitute a potential emergency, and should be evaluated in an er.

Actually uncommon: Serotonin syndrome gets a lot of mention, but is actually more often a potential problem than a clinical issue. Concerns with certain medications and drug interactions seem to highlight the category. Best you discuss your current and future medications with risks in mind. A conference with your doctor should answer all of your concerns.

Serotonin syndrome: Depends on severity. Needs early detection and intervention as emergency.