Initiating A Sp Makes My Heart Race Like Crazy

Heres what you need to know. Pretty much every week at saturday night I am very tired but cant fall asleep. So the other day i found myself awake in bed at about 1:30 AM and I had an alarm that was supposed to go on at 3 because I wanted to try SSILD. I fell asleep, woke up about an hour later by the alarm, did the cycles and everything but I just couldnt fall back to sleep. Eventually I laid on my back and concentrated on the blackness behind my eyelids. As I continued to concentrate the blackness grew bigger and bigger and took hold of my thoughts. My heart was beating as if I was running a marathon or something. I was sure I was going into either a SP or a LD but heres the thing, I wasnt paralyzed, my eyes flickered like rem, and my thoughts were almost fixated on the blackness ( not to mention the heart thing) but i was still fully aware, nothing happened for maybe a minute, then I got nervous and just opened my eyes and got up. My eyes still acted as if in REM and my heart still beat fast (this took a while to calm down). Last night I also had a similar experience, only I was familiar with the procedure this time and decided to open my eyes almost immediately. So my questions are: A. Did i experience SP? B. How do I transition from said experience to an LD. C. What's up with the heart thing?, is it at all dangerous? Thank you for reading. Any advice will be appreciated. TLDR: Can Initiate SP, might have a heart condition :)