Answer: It is not normal for the tree to defoliate, and based on your description it is possible it is dead. The three main causes for a citrus tree to lose its leaves would be overwatering (in winter especially), underwatering, and a pest/disease problem. Without seeing the plant while it still has some leaves, it is difficult to trouble shoot. If the tree needed repotting or had an untreated pest or disease problem, that might have killed it. I'm really sorry about your tree.
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