It has been four days since I had my wisdom teeth taken out. I was brushing my teeth on the fourth night and I hit one of the sites of extraction. When I spit blood started to come out but it stopped a few seconds after. Did I lose my blood clot ?

Kind of difficult to say from your description. There would still be a small amount of blood involved around the gum line from an extraction. Doesn't necessarily mean the clot came out. Can you see a dark surface in the extraction site?