Why is it called a slumber party when there is no slumber?

I'm confused. Disoriented. I find myself in a whirling dervish of giggles and excited shrieks. The smell of nail polish is in the air, and hair scrunchies are flying. The scene feels oddly familiar, like that of a distant memory I've tried to block out, but also very very different.

I'm at a slumber party. 

In Paraguay.