Part of the reason he is so carefree about the whole thing is that Diarmuid doesn't consider himself a captive or someone who has been kidnapped. Instead, he considers himself a visitor who is here to help people who need help. Maybe he is more easily able to view things this way because he has been home and back before...

Diarmuid nods, and then his expression growing sad, "When I was sent back before, I didn't remember being here the whole time I was home. When I came back, all of my memories came back. I don't understand how that works. How do you erase something someone has experienced so completely? Father blocked the memory of that night from me, but I know it's missing. When I was back home, I didn't think anything was missing even though I didn't remember this place at all!"

He pauses and shakes his head, "I don't like it. I hope it is just happening because of the power issues they are having here. Maybe once we have fixed that, we won't have to worry about forgetting this place anymore. It's one more reason to help, right?"