Oh goodness. So sorry and sad to hear that. Sounds like it may have been Cocci though there are a wealth of other nasty ailments I haven't had the joy to experience yet. PM perhaps for your own peace of mind?
I would have thought that cocci in an adult sheep is really, really rare - after all the bugs are around in the soil all the time and it's usually lambs that get ill with cocci as their system is not used to them yet and so they haven't built up an immunity.
It is also almost impossible to confirm coccidiosis, as even normal and healthy ewes have a high amount of coccidia in their systems, only a specific test to distinguish between the good ones and the bad ones would make a diagnosis possible.
I also wouldn't have thought that death would be that quick, I have a couple of goat kids every year that keep coming down with Coccii a few times until they are 6 months old, and even though they have scours they are otherwise bright and breezy.