A similar thing happened to me. Astarion presumably drained me dry as the screen faded to black. Then I am alive, waking up at camp, with Shadowheart dead in her sleeping roll in a pool of blood. I talked to Astarion and he said that he already apologized (for killing me?). There is a combination of missing cutscenes and dialogue and/or a bug where Shadowheart dies instead of the PC.