help me out. Death metal vocalist here.

My friend said there's a trick to screaming/growling that lets you do it without hurting your vocal cords and losing your voice, does anyone know about this?
 
I find that if I do not practice my vocals all the time and then I just jump into it I do get light headed and a sore throut. But when I am practicing all the time, even while driving in the car I never have any issues.

Peter