Why does zoloft (sertraline) 100mg cause an acute oculogyric crisis?

Usually it doesn't: Zoloft (sertraline) inhibits serotonin reuptake, and in that way can also affect dopamine. The resulting increase in serotonergic activity can inhibit both nigrostriatal and tuberoinfundibular dopaminergic neurons, resulting in extrapyramidal symptoms (eps). Balance between these systems is extremely important. Akathisia is the most common kind of eps from zoloft, (sertraline) rather than oculogyric crisis.