Derek had not understood. He would not lie. At first when Emily had been talking about an auntie, and a visitor. He had really thought that either he was still asleep. Or she was the one who was talking in her sleep. But then when she had finally said exactly what she meant, he had freaked out. No lie, internally he had been running a mile a minute. Trying and failing to come up with something to say that would not be offensive. Not only that, despite knowing that periods were a normal monthly thing that most women went through.
Derek's mind had somehow decided that Emily needed to be in the hospital for such a thing. That she needed urgent medical attention. In fact, he had even been readying himself to gather her up, and run outside with her in his arms so that he could drive her to the nearest medical facility.