Amycus was concerned for his sister, but his concern was not limited to her physical well-being in the moment. She had just committed murder - perhaps she hadn't grasped this yet, but he was far more concerned about covering it up than he was about making sure she did not feel any guilt or fear. If he was terrified, it was only right that she be afraid of what might happen as well.
Taking a deep breath, Amycus forced himself to calm, although he covered his face with his hands. "Go to bed, Alecto. I'll have the house elves bring you something to help you sleep, and you will take it. We'll discuss this in the morning, once my head is clear."