The function of this emotion is to alert us to the possibility of danger and push us to make necessary preparations to protect ourselves. Occasional bouts of anxiety are entirely normal and one of the unavoidable costs of being and staying alive. However, when worries get out of control or persist and are accompanied by an array of unpleasant physical sensations like jitteriness and pounding heart, they overwhelm the capacity of the brain to rationally consider the hypothetical danger. Under those conditions, anxiety can get in the way of day-to-day functioning or cause unnecessary distress, at which point it is designated a disorder.