Our first Dead chicken! Sudden, Why?

Hi all!

OMG! We went out shopping for a couple of bits and peices at 11.30 and got home at 1pm and hubbie went down to check for eggs and found one of our best layers dead!
She was still warm and had no marks on her, eyes closed, face purple.
She was only about six months and we checked and she wasn't egg bound or anything!
Really quite upset, why?
I just hope she wasn't suffering and we didn't know. They were all let out at eight this morning as usual and everything was fine.
Do they get heart attacks?

Any opinions welcome,

Thanks Carrie.

So sorry to hear about your hen

xx