Answer: Based on your description I am not certain what has happened to your lantana. If you plant to keep it in active growth all winter it is best to bring it indoors while outside temperatures are still in the 50's. If you plan to store it "resting" you would bring it indoors while temperatures are still in the mid 40's.
It is possible it has been shocked by the abrupt change of temperature from outside to inside, or it has tried to go dormant due to being outside in cooler weather and shortening days, or it may have suffered from exposure to too much cold if it was frozen before you brought it in.
You can check it for live vs. dead wood beginning at the branch tips. Live wood is flexible and has green inside the bark, dead wood will be dull colored, dried out, brittle and snap in your fingers and will have no green inside. Cut it back to remove any dead wood and then as needed to restore a bit of symmetrical look to it. The hard and crunchy leaves are dead and can be stripped off.
At this point, if it is still alive, I would suggest you put it in a cool room (temperatures about 50 to 60 degrees) with very bright light; water just enough to keep the soil just slightly damp -- not soaking wet but not completely dried out. Allow it several weeks to adjust to the new location and hopefully it will leaf out again. Once it begins to grow leaves you could provide additional light to total about 16 hours of light daily, if you wish. Good luck with your lantana.
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