Hey OP

I'm sorry to hear you're worrying about this stuff. I know it can be pretty scary, as Serotonin Syndrome is a severe, often life-threatening condition.
I'm going to tell you from a guy on the internet's opinion, I find it unlikely that you're experiencing Serotonin Syndrome given your description of your current drug usage. Serotonin Syndrome can happen at seemingly random points to different people. In general, if we're talking about substance-induced Serotonin Syndrome, it's generally gonna occur in folks taking multiple medications in moderate-high dosages or otherwise just a very high number of different medications.
Opioids are not known for their effects on Serotonin. Neurotransmission is a complex process with many variables. However, it's my understanding that the primary neurotransmitter at play here would be Dopamine. It is likely that other neurotransmitters might be released as a secondary effect, being that this is a psychoactive drug, however, Serotonin is not a major player here.
You mentioned you have anxiety. This can convince people of a lot of different fears and possibilities. I find what's most helpful in these situations is to get some more objective information. Do some research of your own. Listen to what the smart people have to say. I think when you read some case studies and see the common causes therein, you'll realize that your situation is unlikely to produce Serotonin Syndrome. I'm not saying it can't, just that it's unlikely.
For the record, Serotonin Syndrome as I've read and heard it described by many survivors and doctors, is not something that a person typically questions when it's happening. In general, it seems to be an extremely distressing, painful and disorienting process on par with something like a heart attack. It's not something so mild that you can sit and question it for hours, check in on Bluelight and be okay.
Continue to monitor the situation and if shit gets extreme call 911 before consulting us. Just to be real, the time it will take for us to answer could lead to serious injury or death.