It's very possible, after briefly starting on Prozac which was a SSRI (Selective serotonin reuptake inhibitors) and looking up several thread along with what my personal experience is and currently at I wouldn't doubt it. Not to mention my immune system is crap compared to before this whole spiral. People think Serotonin starts in your brain but is actually constructed in your GI track, why do you think when people undergo LTC they tell you to eat healthy and to stay away from things that can be toxic to your digestive system such as sugar or processed food. Ever since I changed my diet and got on SSRI things have progressed from what they where 2 months ago, but is all a case by case basis I'd have to think. Many have different things going on with them but Serotonin does play a huge factor on what you may feel and what you may have going on.