a person who worries all the time about their health and believes that they are ill when there is nothing wrong with them; a person who suffers from hypochondria疑病患者
Don't be such a hypochondriac!—there's nothing wrong with you.别这么忧心忡忡的了!你根本没病。
Word Originlate 16th cent.: coined in French from Greek hupokhondriakos, from hupokhondria, denoting the soft body area below the ribs, from hupo ‘under’ + khondros ‘sternal cartilage’. Melancholy was originally thought to arise from the liver, gall bladder, spleen, etc.