About two weeks ago, I did an RC and found out I was dreaming. Naturally, I was excited that it worked, but I felt the dream starting to fade. I quickly tried keeping myself in the dream, but suddenly, it felt like I was spinning around really quickly and my heart felt like it was beating very quickly. I was pretty freaked out about that and my friend told me it might have been an episode of SP. Is this what it feels like?
Mmh, doesn’t sound like it. SP is the fact of being paralized and conscious, some people get fast haertbeat indeed.
But in this case it just seems like a pretty common feeling you get when you wake up from an LD. 
Sounds more like a FA to me. SP is when you cannot move at all, and you know you can’t move.
Probably it was because you were too excited from getting a lucid dream and subsequently woke up really soon. Just try to remain calm and cool, and you’ll be fine. Also try to stabalize yourself within the dream, by looking at your hands or by rubbing them together.
You have sleep paralysis every time you sleep, if you are ever concious during it, there will be no question if it is SP or not because you WILL NOT be able to move.