I apologize for this delayed reply to your gardening question and hope it is still helpful to you.
That is strange. Those plants are prone to wilting in too much sun and to droughty conditions in general. Yours might be also dealing with some type of fungal or bacterial blight although such in very uncommon with Angel's Trumpet. I suggest you contact your County Extension Service to see if they can diagnose a plant sample for you. It also may be that the plant just needs the damaged areas pruned away and with some fertilizing and watering will be fine.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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