I have had my cactus for about 10 years. I have had it in the same window (south) for all that time. It blooms beautifully every year and did so this year. But for the last couple of months it has been molting leaves. It has lost about half of its size. What remains looks healthy, but every day I come home to a few more sections on the floor. What is the problem? Nothing else I can think of has changed.