has anyone ever experienced serotonin syndrome?

Yes.
If a person has the gene for bipolar (i do but it's a mild version) - then taking an SSRI for too long
(varies according to the person) - results in somewhat pre-manic behaviours:
loss of fear and caution, leading to behaviours like
not wearing a seat belt and crossing the median line on blind corners,
with no brindle or halter, getting on the bare back of a two-year-old unstarted filly... getting bucked off and damaging the eye on sharp gravel
spending too much money,
feeling euphoric and enthusiastic,
getting loads of creative ideas,
becoming impulsive.

Thankfully not. I've accidentally taken double doses of my medication without issues. I think it would take a good amount more for me. I don't want to find out though.

I think dainbramadge has that i get depressed as fck sometimes, so I can only imagine what it must feel like to have No serotonin flowing through your system it must be hell.

Hell on Earth. Confusion. Tightness. Anxiety. Never taking antidepressants again. I don't trust the psyche industry in the US.