Insufficient sleep is commonplace, and understanding how this affects interpersonal conflict holds implications for personal and workplace settings. We experimentally manipulated participant sleep state for a full week prior to administering a stylized bargaining task that models payoff uncertainty at impasse with a final-offer arbitration (FOA) procedure. FOA use in previous trials decreases the likelihood of voluntary settlements going forward—the narcotic effect. We also report a novel result that a significantly stronger narcotic effect is estimated for more sleepy bargaining pairs. One implication is that insufficient sleep predicts increased dependency on alternatives to voluntarily resolution of interpersonal conflict.