 Conceptually, interest in dreamless sleep experience has been facilitated by the precise definition of dreaming offered by simulation views (Revonsuo et al. 2015). If dreams are immersive sleep experiences characterized by their here-and-now structure, it makes sense to ask whether this is true for all or just a subset of sleep-related experiences and whether non-immersive sleep experiences exist. By contrast, if dreaming is broadly identified with any conscious mentation in sleep (Pagel et al. 2001), there is no conceptual space for dreamless sleep experience.