Both 癫 and 狂 carry the 疒 'illness' radical (癫) and 犭 'animal/beast' radical (狂) - clinical madness on one side, animal wildness on the other. Together they mean 'lost-mind frenzy', covering both medical mania and over-the-top excitement.
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Used both clinically (癫狂症 'mania') and loosely ('frenzied/wild'). Lighter synonyms: 疯狂 (fēngkuáng, much more common), 狂热 (kuángrè, 'fanatical'). 癫狂 is more vivid and slightly literary - picture someone truly out of control.
