I believe the physiological sensations brought about by the "letdown"
reflex may cause some mothers anxiety.  The fear then triggers a
psychological response.  Post-partum is an ideal time for
many women to experience panic and depression in any case.  One mother
I counseled last week just went through an expensive battery of heart
tests that showed nothing.  These feelings of panic very quickly can
snowball until the mother becomes phobic.  Please encourage her to
seek therapy ASAP!  Also reassure that panic attacks are actually
harmless although they feel like the world is ending.  An excellent book
is
The Feeling Good Handbook by Dr. David Burns.  I know it is available in
England and the States.

Susan Nachman-Srebrnik, IBCLC