Doris,
I know this is not as concise an answer as you were looking for, but there are a number of causes and you'll have to look at a number of issues. Did you use a magnifying lens to look for spidermites or other pests? If you can't find any even with a magnifying lens, it is probably a nutrition problem. Have you looked up Tonny's thread on nutrition on DG?
http://davesgarden.com/communi...
Unfortunately, Tonny's photos don't appear any more. It's too bad because they were very instructive. However, I do have my copy of Tonny's e-book on Brugmansias. In it, one of the first things he suggests is to check the potting mix's pH. If the soil is too acidic or too alkaline, nutrients get bound up and are not available to the plant. Tonny includes a chart in his e-book that lists deficiencies that can result depending on the soil pH. If the soil pH is below 6.5, then your Brug could be suffering from deficiencies of any of the following: Boron, Phosphorus, Potassium, Calcium, Nitrogen, Magnesium, Molybdenum, or Sulfur. If the pH is above 7.0, then the Brug could suffer from the following deficiencies: Phosphorous, Nitrogen, Copper, Magnesium or Zinc. Sometimes, getting the pH back to between 6.5 and 7.0 takes care of the nutrient problem. Adding Calcium carbonate or dolomitic lime will raise the pH. Lowering the pH is much more difficult and in that case it is best to replace the soil. PH of the soil has to be corrected first before you try adding any nutrients.
If the soil pH is where it should be, then adding the needed nutrient will correct the problem. You didn't mention if the leaves that were curling were new or old leaves nor whether you have fertilized you plants since you took them indoors. If the curling leaves are the new leaves, then there is probably a calcium or calcium/potassium deficiency.
You also have to examine the Brug's environment. Sometimes, cooler temperatures and low light can cause a Brug's leaves to curl. Several environmental other issues can also cause the leaves to curl.
IVeronica