Are you in the United States? Just trying to figure out if your temperatures are in degrees F or C. What did the temperature actually drop down to, was there any frost? Is this Euonymus fortuneii?
In addition to the things Elaine said to check, can you look at the undersides of the fallen, and still attached but droopy, leaves with a magnifying lens for spider mites. I notice some of the leaves at the branch tips look a little distorted and cupped, so just want to eliminate a potential pest problem (they can be hard to see - look also for webbing and eggs).
