Strange things happening to Caribbean Fish

Recently I've had a Bi-Color Pseudochromis and a Royal Gramma die on me.
They were not in the tank together. About a month ago I found my Royal
Gramma (which I had kept healthy for six months) stuck between 2 pieces of
live rock. He was dead. The strange thing was he was stuck head first
between the 2 rocks. I really had to pull on it to get it unweged. It was
really strange. I've never seen anything like it. It's almost like the
fish committed suicide. The carcass showed no signs of disease and he ate
fine earlier that night.
I replaced the Royal Gramma with a Bi-Color Pseudochromis. He has been
doing fine and today I saw its rear fin sticking out a hole in the rock. It
was the same deal, he was wedged in there and I really had to pull to get it
out. The fish was dead but it showed no signs of disease or trauma. All
the other livestock is doing well in the tank. The other fish are a flame
hawk, maroon clown, damsel, and a Yellow watchman goby. I also have a
cleaner shrimp.
Does anyone have any ideas on why these fish seem to be acting this way to
cause them to die?