Well, it's a sign that the plants aren't getting enough light, and if they don't get enough light, they cannot photosynthesize properly, meaning they don't have enough energy, and worst case scenario eventually will probably start to give up on existing. (Best case, they'll just look really sad). I'm putting in another vote for some supplemental lighting. I agree also that some of those plants look a bit more moist than they should be during the winter (hawthoria being an exception, as DragonsEye mentioned. Some aloe too, if I'm not mistaken).
Originally Posted by h.the.cvt