Attested in the Yuan drama 《碧桃花》: '不由我不心惊胆战,索陪着笑脸儿褪后趋前' — 'I couldn't help but quail in fear, forcing a smile as I shrank back'. The gall (胆) is the traditional Chinese seat of courage; a trembling gall = fear from the inside out.
culture
In Chinese medicine and folk psychology, 胆 (gallbladder) is the organ of courage — hence 胆大 ('brave') and 胆小 ('timid'). A 'trembling gallbladder' is not metaphor but anatomy.
