Answer: Based on your description it is uncertain whether the plant has simply defoliated in protest or given up the ghost. If it is still alive it may releaf out.
When brought indoors, this sun loving plant does best in a very bright location away from drafts, but may lose a few leaves (or more) normally during the adjustment from outdoors to indoors. If there is enough light to keep it growing actively (as in a greenhouse or conservatory), the soil should be kept slightly moist and the plant may be fertilized lightly according to the label instructions.
If the light levels are relatively low as they usually are under average home window conditions, the plant should be kept somewhat cool and watered just enough to keep the soil from drying out and no fertilizing. The plant will then rest until spring.
In spring when the days lengthen the plant will show signs of actively growing again. This is the time to repot if needed, resume fertilizing, and trim it back if needed to control size.
Some typical problems to watch for are white flies and spider mites, both of which thrive in indoor overheated and dry conditions and can be treated with insecticidal soap according to label instructions. They may cause yellowing and leaf drop if untreated.
I hope this helps you troubleshoot and I hope your plant recovers. If not, please don't feel too bad. More shold be available this spring for the summer patio season.
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