It started off with feeling excessively drowsy to the point of dozing off for a while. I woke very suddenly some time (dunno how long but not very long) later feeling extremely stimulated, hot and sweaty. A bit manic really, and starting to feel a bit confused. At this point I started to march back and forth to work off some of the excess energy and stripped nekkid whilst I was at it cos I was so stupidly hot. It all gets a bit patchy after that but the bits I recall were...
Delirium: I thought I was a pagan storm god and I could very clearly see the world laid out below me (complete with mountains and oceans and weather and stuff) and it was my duty as stormgod to bring rain (yes, to wash away the filth and the scum etc). This involved a lotta pissing. A helluva lotta pissing for most of the night. Place was a fukkin mess the next day I can assure you.
Convulsions: At times I was flexed backward to such an extent I thought my spine would surely snap - really was virtually able to touch my heels with the back of my head at times. This was not pleasant. At all.
Pain: This was beyond imagination. I still can't believe it's possible to be in so much pain and not actually die. It was truly indescribable so actually can't describe it. Whatever you are thinking, it was a helluva lot worse than that. If I'd been capable of action I would have killed myself on the spot without a second thought just to make it stop.
Aside from that there was the overheating and sweatiness which was truly extreme but I have no way of quantifying that other than I was rather hot and bothered to say the least. But mostly it's all a blur of pain, convulsions and delirium. And pain. Above all there was the pain. And the madness. That was also quite the feature. Oh, and the convulsions. They were hard to ignore. And the pain. Oh fuck yes the pain... It lasted a few hours but thankfully I only remember brief flashes.
AFAIK, SS is an acute reaction to excessive serotonin - essentially acute serotonin poisoning