The Bible says Jesus sweat blood, but the  Book of Mormon and D&C clarify that He sweat blood from every pore (see Mosiah 3:7 and D&C 19:18) 

Bleeding from the pores is a rare condition called hematohidrosis (source). What caused this? 

President Brigham Young taught: “At the very moment, at the hour when the crisis came for him to offer up his life, the Father withdrew Himself, withdrew His Spirit, and cast a vail [sic] over him. That is what made him sweat blood. If he had had the power of God upon him, he would not have sweat blood; but all was withdrawn from him, and a veil was cast over him, and he then pled with the Father not to forsake him.”[Source]