A BP going off feed (especially during the winter months) is not uncommon. Having last eaten 16 days ago, your BP should not be losing weight. Many balls have been recorded to go off feed for months (i.e. 3, 4, even 6 months) at a time. My BP had suddenly decided he didn't want to accept his usual rat offerings about 3 weeks ago as well and hasn't eaten since. Just continue offering your BP every week (or on his usual feeding schedule/day), and so long that your BP hasn't lost noticeable weight...there is nothing to worry about. Are you actually measuring his weight? The general rule of thumb is that if indeed your BP is losing body weight, a trip to the vet would be recommended. Otherwise, don't sweat it!