bottom leaves turning yellow and falling off -- very slowly

On my poinsettia, which I have had in my office for about 2 months, the bottom leaves have, one at a time, begun to turn yellow and then fall off. They aren't falling off in droves, or even in 2s and 3s. Is it because I am not checking and watering often enough? So far, only 2 leaves have fallen off and 2 more are in some stage of yellowing. I can't think of anything else I could do to make the plant happy. I welcome any suggestion you may give.

Doug says that this plant is unhappy - probably with the amount of sunlight it's being given. And in an office is out of it's comfort zone of full sun in Mexico.

The reality is that this shrub isn't designed for long term indoor use unless you're a berserker gardener with grow-lights (always assuming you don't want a tall lanky plant).

My .02. Toss it - make your office look better.

But to answer your question - it's plain and simple plant stress, trying to grow something in an area it isn't suited for. (and light is the number one reason for slow leaf drop)