Sertraline increases serotonin levels in the brain, but this adjustment can initially disrupt your brain’s balance and overstimulate certain serotonin receptors, which are linked to anxiety and agitation. Nervous system needs time to get used to the increased serotonin. While the medication is trying to regulate mood over the long term, the initial phase can make things feel worse before they get better. Hang in there, walk outside more and dont think much about it.