Sometimes the word hypnagogia is used in a restricted sense to refer to the onset of sleep, and contrasted with hypnopompia, Frederic Myers's term for waking up.[1] However, hypnagogia is also regularly employed in a more general sense that covers both falling asleep and waking up, and Havelock Ellis questioned the need for separate terms.[2] Indeed, it is not always possible in practice to assign a particular episode of any given phenomenon to one or the other, given that the same kinds of experience occur in both, and that people may drift in and out of sleep. In this article hypnagogia will be used in the broader sense, unless otherwise stated or implied. -Wikipedia