Hi Daisychain,
Thanks for your question and being part of our discussion forum! Being in pain is exhausting and frustrating, I'm sorry you are experiencing it.
Many of us, myself included use Imitrex (generic sumatriptan) or a different triptan and an SSRI and haven't had an issue with serotonin syndrome. I use Celexa daily and sumatriptan nasal spray no more than twice a week (to prevent rebound or medication overuse headache) and haven't had a problem with it. Having said that it doesn't mean it can't happen, but is pretty rare.
Don't hesitate to discuss this with your doctor and/or pharmacist, they are a great source of information!
Nancy