HI or HH hypnogogic images or hyponogogic hallucinations are the things you experience while trying to pull off a WILD, like sounds and vibrations. They often happen about the same time as SP, but are not related.

SP does not mean you can not move (unless you have a rare sleep disorder), it is just a state that happens in sleep. It is a chemical effect your brain creates that makes you less likely to act out your dreams. Because you stay aware while your body falls asleep, in WILD attempts, you can actually feel when the chemicals release, if you know what to look for. It is used as a marker for how close you are getting to a dream state. However, SP does not keep you from moving using your concious will, so you can never test SP. If I am in SP, I get a sedated narcotic feeling and moving would take effort and intent, but I can break the SP in a second if I need to move. The problem is when beginers want proof they reached SP, so they try to move, and disrupt their WILD attempt.