Loubylou, you've posted this question 3 times, and I answered the first time round. Leaves which yellow, from whatever cause, usually do drop off because the yellow colour indicates they're dying.

Keep the roots moist but not soggy and hope for the best.

If it's just a few, they may just be old leaves--evergreen plants shed their old leaves little by little. If it is more than 15% of the foliage, I would suspect drought first, and poor drainage second. Your watering history will tell you quite a bit about that. Barring that, sometimes a severe infestation of aphids or their kin can cause that. More rarely, a serious nitrogen deficiency--maybe caused by too much raw forest products as a soil conditioner--can cause the entire plant to look a tired, yellowish green, and the oldest leaves will turn and drop.