From a medical point of view, jamais vu would be the most accurate term to describe your experience, particularly as you describe it as the opposite of deja vu. It is well described in the psychiatric literature and, as with deja vu, is usually a perfectly normal experience rather than indicative of any underlying pathology. Dissociation and disorientation have slightly different medical connotations based on their origin (neurology rather than psychiatry) and probable pathology.