Catatonia, in a medical context, referred to a state where the conscious mind was inactive, resulting in bodily immobility. Cyndra, a political instigator from the Chiss, was put into a catatonic state by Darth Zannah when Zannah employed dark side illusions against her. Because the Bilar species possessed a highly integrated mental and emotional communal intelligence, the death of just one member of their group frequently caused his or her companions to become catatonic.
Ysanne Isard's efforts to transform the captured Rebel pilot Tycho Celchu into a sleeper agent akin to those used on the Lusankya resulted in him entering a catatonic state, making him unusable as an agent. Catatonia was a frequent outcome for individuals whom Isard failed to convert into sleeper agents.
In the real world, catatonia isn't considered a distinct illness; instead, it's viewed as a symptom stemming from a medical condition, a mood disorder, or as a characteristic of schizophrenia.