New to mice. My son got two for Christmas, one turned out to be pregnant so the shop kindly took her back, introduced a new one who seemed fine at first, a bit of chasing/biting from the resident doe (who is very energetic and healthy looking) but they started nesting together. Within a couple of days the new mouse has become almost completely inert, hunched, occasionally creeps around a little but for the last day or so we haven't seen her eating or drinking, and now she has one eye closed. Really worried. Any thoughts?