We present an analysis of the use of diagnostic labels such as "seizure", "attack", "fit", and "blackout" by patients who experience seizures. While previous research on patients' preferences for diagnostic terminology has relied on questionnaires, we assess patients' own preferences and their responses to a doctor's use of different labels through the qualitative and quantitative analysis of doctor-patient interactions in a realistic clinical setting. We also examine whether two sub-groups of patients--those with epileptic seizures and those with (psychogenic) non-epileptic seizures--show different behaviours in this respect. Our findings suggest first that patients make fine lexical distinctions between the various diagnostic labels they use to describe their seizure experiences; secondly, that patients play an active role in the development and application of labels for their medical complaint; and thirdly, that attention to patients' lexical choices and interactive use or avoidance of labels can be relevant for the differential diagnosis of seizures.