What Causes Fainting After Getting Finger Hurt?

i was going to use the bathroom and jammed my finger in the door. berally bad enough to bleed. it wasnt that bad but after i got done using the bathroom my head started spinning and the pain in my finger intsified and pulsed worse and worse till i started to loose my sight then fell back flat like a board. i jerked back awake and was sweating and over heated it seemed.