My first thought was like Rebecca says. I see old leaves go pale like that then drop off, but new growths replace them.
However yours seems to be doing it more extensively than mine, so my second thoughts were moisture, and my third thought was light.
It's possible if it's not very happy then it's sacrificing leaves on the already bloomed growths (which do die back eventually anyway) maybe a bit quicker than it would if conditions were perfect... or maybe it is just normal old growth die back
I would try repotting, I like to do mine every couple of years. I like to pot in a mixture of potting compost, bark, and perlite and grow it almost like a standard house plant.
I've had growths go mushy at a point and dye off. I don't fully know why I'm afraid. I find that if the plant is happy that still might happen, but it will be growing enough to make it not matter much.
I keep the compost always just moist but not wet, it seems to grow well that way. It can even grow in a vase of water with no medium, that's a good way to root pieces that fall off in fact, so I wouldn't worry too much about keeping it moist.