Magnesium deficiency, AKA "grass staggers" - basically in this kind of weather the grass grows too quickly to pick up enough enough of certain minerals, leading to a deficiency in the sheep
They can't build up stores in the body so have to have enough each day.
Calciject has magnesium in it, so your neighbour did the right thing, just too late by the sounds of it (not a criticism - it happens so quickly)
Get some mineral licks in the field, apparently they don't like it "undisguised" so it needs to be in a mix with molasses and other goodies.