Hard to know about second hand information.  However, what this sounds like
is a myoclonic jerk (the seizure like activity, not the neurologist).  Most
of you know what myoclonic jerks are, since, sometimes, as you fall asleep,
you have one, often while you are dreaming of falling down, or tripping or
something like that.  They are benign.  The upper arm of the baby might be
affected alone, as they would be inhibited by restraint (the lower arm
pressed against the mother, perhaps).

If in doubt, blame it on the breastfeeding.

Jack Newman, MD, FRCPC