Be extremely anxious (5)
(Other definitions for sweat blood that I've seen before include "Be very anxious" , "work extremely hard" , "Strenuously work" .)
(Other definitions for sweat that I've seen before include "Salty fluid secreted by the body" , "Waste (anag.)" , "Salty fluid secreted by glands" , "Soldier" , "Trouble in Australia" .)