My sand cherry tree was growing perfectly fine until
yesterday. All the branches drop down in one day. I
have no idea what happened. I was thinking could it
because of the rain from yesterday? Our neighbors'
gardener also came yesterday for their garden
which is right next to us. Was also thinking could it
be possible for them to accidentally put weed killer
or something that would cause this?

Attached two photos for comparison. Left is picture
when it was healthy, right is picture from today =(

Please help to save this tree!