nothing to worry about. Plants often, depending on variety, begin to cut off and drop their lower leaves so more energy goes into the new top leaves. I just pick them off when they yellow. Puu Kahea and Celadine do this mid summer often. Others do only a few leaves.

I had similar as a single leaf on a couple plants, and I just snipped them off and disposed of. The plants seems to be growing and flowering happily. Mine were generally the lowest leaf. I'm asumming this is what tdogdad said.

Thanks for the reassurance; I'll stop hyperventilating now :-)