Help with dragon age characters?

My characters keep randomly dying. They will all have full health then all of the sudden out of no where they fall over dead. From what I can see they had no injuries that needed healing. This isn't the first time this has happened while I was playing. Why are they suddenly dying like that and what can I do to prevent it. Also it's not cause the opponent is too strong. They will kill over dead even without being hit.Help with dragon age characters?
Get the patch.

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