I had almost the exact same thing happen a couple weeks ago with my platy. I believe she swam into the open end of my cholla wood log. The she tried to turn around, and her head stuck out a hole on one side of the log, and her tail stuck out a hole on the other side of the log. She was really tight in there. I don't know how long she was there, but I was able to use a pliers and break away wood to free her. She was injured, and died during the night. I think it is simply the stress of being stuck, kind of like shock in a person.