Grosse Point Farms Fatigue: Fatigue or stress causes your cortisol levels to be elevated, and this anti-inflammatory effect becomes too strong. This effectively stops your immune system from working as it should, and this weakened state can last for whatever is causing the stress. Fatigue or stress causes your cortisol levels to be elevated, and this anti-inflammatory effect becomes too strong. This effectively stops your immune system from working as it should, and this weakened state can last for whatever is causing the stress.