I purchased my begonia rex on the internet and it came in ok, few leaves dropped but not too many and it was doing fine for a while and had a new leaf coming out. More leaves dropped and a few days ago it got down to 58 degrees and all the leaves dropped. The thick part where the leaves came out of is fine, is it dying or dead? has it gone dormant? what do i do?

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the orange bowl is filled a bit with water for humidity and it's standing on a raised cup thing above the water.