Sprained my ankle & then almost passed out but felt no immediate pain?

Last night I was sitting on the edge of my bed and (stupidly) decided to try to walk on feet that were very much "asleep." My feet/ankles were so asleep that when I slid off my bed and landed (my bed is high so I can't touch the floor) on the side of my left ankle. I heard it crack at least twice and landed on my knees. My feet were still asleep so I couldn't feel it hurting but I could feel my heartbeat in my left foot. I don't know if it scared me or what, but I noticed I was hyperventilating and I tried to calm myself down but I couldn't. I yelled for my mom and she and my sister came in there. When they got there, my vision was getting foggy and it sounded like they were miles away. I couldn't feel anything I was touching. They told me my eyes were rolling back and my pupils were huge. I lost all the color from my face and my lips turned blue. Then my sister gave me some cold water to drink at that stopped me from passing out. My vision returned and then my hearing went back to normal but I had a ringing in my ears for a few minutes after. This was last night, and my ankle is still very sore and swollen, but other than that I feel fine. I just don't understand why spraining my ankle would cause all that? It's not like I blacked out from the pain because I couldn't even feel it! If anyone could help, I'd really appreciate it.