Anxious dysthymia is a subtype of persistent depressive disorder that is linked to low serotonin levels in the brain. Low levels of serotonin can disrupt emotion regulation and relaxation during stressful events. The most prominent symptoms of anxious dysthymia include low self-esteem, self-doubt, rejection sensitivity, increased agitation, and the possibility of developing insomnia. When the individual who suffers from anxious dysthymia are under stress, their symptoms get worse.