noun

a state of despair, typically one which results in rash or extreme behaviour.

she wrote to him in desperation

hopelessness,despair,distress,anguish,pain,agony,torment,torture,misery,wretchedness,disheartenment,discouragement,resignedness,forlornness,defeatism,pessimism,recklessness,rashness,impetuosity,foolhardiness,riskiness,audacity,boldness,wildness,imprudence,injudiciousness