Fainting Spells When In Pain Since Childhood. Turn Pale And Shaky Before Fainting. What Does This Indicate?

Ever since I was little, I faint or pass out because of pain or sometimes because of extreme heat from being outside. It's continued into adulthood and just the other day I twisted my ankle and passed out, woke up and passed out again. People tell me when I do I turn white and most of the time I shake. While having a tooth extracted a few months ago, I passed out in the chair, but I couldn't feel any pain. My friend told me that right before I faint I turn white as a sheet of paper and then my hands and legs kind of curl inward and then I go limp. Right before I faint I feel very sick like I'm going to vomit and then everything goes black. When I come to, I am usually sweaty and have to lay there for a few minutes before standing up because I feel sick. I've been like this every since I was a child. Can you tell me what is happening?