Hughlings-Jackson coined the concept of dreamy state: According to him, one of the sensations of a "dreamy state" was an odd feeling of recognition and familiarity, often called "deja vu". A clear sense of strangeness could also be experienced in the "dreamy state" ("jamais vu"). Jackson himself did not use these French terms, but he was quite clear about the vivid feelings of strangeness and familiarity, which can occur in both normal and pathological conditions. In order to explore some of the exchanges between medical and nonmedical vocabularies, we examine the historical origins of this technical concept. By basing the study on European (medical and nonmedical) literature of the nineteenth century, we review the first descriptions of this state and compare them with the famous Hughlings-Jackson definitions. It appears that this medical concept was partly borrowed from a wide cultural background before being rationally developed and reworked in the fields of neurology and psychiatry.