I havn't had a WILD that I can remember before, but I have played around with some quite vivid visualisation prior to falling asleep. For example, I'll be lying in my bed, eyes closed, thoughts wandering, and suddenly I'll realise that there is an apple in front of me in surprisingly vivid form, i.e. not a hazy thought but an actual vivid image. I then try to focus on it and for 2-3 seconds I can examine the surface of it and then it fades. My body is awake throughout the whole thing. I know that I have not fallen asleep, but I must have been very close in these cases and by the sounds of it quite close to entering a WILD.

The apple is just an example. It could obviously be anything.