Hopefully, it just due to the recent frost. These plants are prone to dieback and phytohpthera infection, so just keep an eye on it. If the part that's drooped dies back, cut it off. Otherwise, there is nothing you can do.

it could well be frost damage. if it is then there is nothing you can do except wait and see. is it in the ground or in a pot. is it particularly water logged, that would certainly cause a problem. if it is try forking the ground to see if you can aid drainage.

It could also be wind-burn which seems to affect different trees in different years. One of our acers that has been in this spot for eight or ten years has suffered some wind-burn for the first time.

I also think it was the weather. Some of my Acers have lost all their leaves - it was the cold wind back at the start of April that did it. The wind came from the north rather than the SW and they got exposed. I looked at the leafless ones yesterday and they are still green under the bark and they may releaf as they have reserve leaves. I did notice that the soil was compacted in mine with all the rain so I gently forked it and added some ericacious feed. Good luck.

Thanks to you all for your prompt responses. I really appreciate your help as I am a very amateur gardener!

p5akos