My Nan Is Dieing And Has Been Given About Two

My Nan is dieing and has been given about two weeks to live, I'm 19 and have never lost anyone particularly close before. I don't seem to be grieving much, not feeling much of any thing really, I occasionally, when I think about I get sad but mostly there is nothing. The only thing that has really changed is I really don't want to turn the lights off at night, is this normal? Is it OK to leave them on? It seems a bit childish and I am trying really hard to be a child in all of this. And it is going to go away right? Because I don't much fancy spending the rest of my nights with the lights, if nothing else it would be a massive waste of electricity