As a part of an experiment I'm currently conducting I'm interested in knowing if the WILD transition phase (hallucinations, vibrations, etc) are present every time a person falls asleep or not. Do these symptoms exist only because people retain their awareness (thus they are caused by awareness) or do they exist regardless but we simply forget them?

I've been searching the internet, but couldnt find any specific case studies.

Anybody got an answer/link/suggestion/personal experience that might shed light on the issue?