I might be a little late on this, but I have had the main stem break near the top. It was my fault for hanging something on it to bend it down so it wasn't hitting the light. So what I did was got a paper towel, moistened it RO water and a small dash of Bloom formula, then wrapped the broken spot with the paper towel then put a small strip of duct tape around to seal the wound and make sure the paper towel doesnt come off when it dries out. About 3 weeks later I removed the bandage and it seemed to heal it self quite well. It didnt hermie on me from stress (thank god), but I am sure the longer you wait to do something, the more painful it is for the plant to endure.
Just get some support on those branches if they're filling up with weight and you should be fine. And if it keeps happening, you may have a calcium def. Good luck!