Serotonin, the happiness hormone, is not something you expect to see connected to Candida albicans. It is something we talk about more in relationship to brain dysfunction and mood disorders.
If we consider that 80-90% of the production of the body’s serotonin happens in the gastrointestinal tract, the distance between the two narrows significantly and a possible relationship between the two makes more sense. Why the GI Tract produces so much serotonin is not completely known yet (motility and appetite are two effects), but a functional link between serotonin and C. albicans has been established, and it’s not about serotonin making candida happy.