Mine is actually going ganbusters! I seriously doubt our humidity is the reason because if my hands are any indication, our humidity level is very low. (Maybe I'll check it later.) I do wonder, however, if mine is going crazy because it is up high. I have it sitting on the hutch of my desk, so it's probably in a spot of the room where the heat is gathering somewhat. Mine is receiving some indirect light, but I don't know whether it would be considered medium light or something else. Here's a picture of my prayer plant today:
..you can see the new growth fairly readily in this. There's sort of an 'upper level' and 'lower level' of leaves. The 'upper level' is all new growth, as is the long, hanging branch (and a few of the leaves near it) on the left.