Falling asleep, and cortical vigilance doesn't fall at a uniform rate, it shifts up and down, tending to becoming lower in steps.  Alpha rhythms rise in bursts but less often and with longer periods of slow waves, and little by little ideas escape us.  In intervals we return to attention realising that we've just had some weird thoughts about something that weren't even related to the thoughts previous to them, and we feel we are talking inwardly to ourselves and that we've just said something that doesn't make sense, or is a made up word or phrase. The voice is accompanied by an equally unfamiliar but striking display of visual imagination.  Faces are common, sometimes moving.  Abstract forms, patterns, nature scenes, becoming more complex, until they are brought to an abrupt end . . .