Can serotonin syndrome occur from just taking viibryd (vilazodone hydrochloride)? i haven't been on any other medicines prior to this but just upped my dose from 20mg to 40mg.

Unlikely: It's possible but extremely unlikely ... If those are the only serotonergic medications you're prescribed. Viibryd (vilazodone hydrochloride) 40 mg. is well within the safe zone of dosages and needs to be titrated up to maximize effectiveness. Hope that helps!

Rarely, but possible: "Full blown" serotonin syndrome usually occurs when a patient taking one serotinergic drug is given an additional serotinergic drug. Most patients tolerate the addition, but due to genetic differences in metabolizing drugs, some patients can become toxic>SS. Mild SS might cause just tremor and hyperreflexia. Severe SS>agitation,disorientation,^pulse, ^^Temp ^BP,Vomiting,diarrhea, ^sweating