From my sample of one.....When I was nursing my babies I was very prone to
plugged ducts and mastitis.  By a process of elimination I found that lying
down to nurse in the early weeks and months lead to  a plugged duct or bout
of mastitis within the next 12 hours. I solved it with my last baby by
always getting cozy in a recliner to nurse at night.  When I was very tired
and tried to stay in bed and nurse, my husband would nudge me and say
remember you need to sit up!  I always felt that the side that was down
didn't drain well, causing stasis and setting me up for problems.
Sincerely, Pat in SNJ, USA