No definite answers for you, but I can tell you I have had similar symptoms, 
along with nausea at MER, while nursing both of my babies.  The closest I've 
come to an answer for myself is low potassium level, but even getting that up 
didn't make it go away completely.  For me, it seems to be a "temporary" 
thing, and improves as baby gets older (finally stopping around 1 year).  I've 
had one client that had the same thing and we never found a definite answer 
for her either.  Like you mentioned, we suggested she nurse lying down, and 
that helped. 

Kimberly Hill, BS, IBCLC
Texas, USA

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