Hi Emily, no need to be afraid! It just sounds like your starter is nice and active, which is a good thing! It's possible that it was a little warmer and further along in the fermentation process when you put it into the fridge, so it continued fermenting and rising even as it cooled down. You might also want to check the temperature of your fridge and be sure it's not running warmer than 40°F, as too warm of a refrigerator temperature could also contribute to a starter that seems especially active. 

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