"Relaxing on command is physiologically impossible if "the body is already too acutely stressed to turn it around," says
Wendy Mendes, a professor of emotion at the University of California, San Francisco, and a researcher on stress. While the body responds rapidly to stress, returning to a relaxed state..."
http://www.wsj.com/articles/why-you-should-never-tell-someone-to-relax-1471370408?cx_navSource=cx_picks&cx_tag=poptarget&cx_artPos=1#cxrecs_s
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