I experienced my first “successful” WILD last night. 
It was a nightmare-ish type dream, so I don’t consider it completely successful. It was only partially successful. You can read the experience and the three dreams that followed in my dream journal.
I just have three questions.
- What is the difference between HI and HH?
- Is it normal to have violent vibrations in the arms (it was almost like a seizure) and violent teeth chattering (I could hear it)? I don’t know if this was real or imaginary either.
- What is a way to stay calm during SP? I panicked last night, I felt like I had lost control. Not fun.
Congrats on your WILD! 
HH is more general, any halucination you get while falling asleep. HI would be only the visual component, just as HS would be the auditory.
Vibrations are common during WILD, I’m sure they were imaginary 
If they weren’t you’d woken yourself out of it!
Staying calm during SP can require practice and getting used to it. Perhaps keep reminding yourself nothing can harm you. focusing on something else can help, like visualizing a peaceful scene…
But if you really start panicing to the point you can’t pull yourself together and stay calm and confident, you can try changing your breath pattern, like breathing really shallow quick breaths (or deep long ones). with this your body will realize your mind is awake and you’ll get out of SP