I have a misunderstanding in human biology...
as its known, when the blood pressure drops in human body, the autonomic nervous system (the sympathetic) stimulates the body to decrease blood vessel diameter, to increase the blood flowing speed, and then return the pressure... but why when this process occurs during blood clotting (spasm), the injured blood vessel diameter decreases to PREVENT more blood wasting, although physically it should increase the blood flow!!!???
Actually, the blood vessels dialate in response to the sympathetic nerve system (you probably got it confused with the parasympathetic nerve system, which leads to vasoconstriction)
Tha's the way our body is built.