I'll spare you the Sparta joke. Partially because I'd hate myself just a little bit for making it.
You get used to it. That's weird in its own right, I know, but it's true. What's even weirder is when you wake up and it's a different era. There was a week over the summer where I spent time in the wild west, the medieval ages, the twenties, a steampunk era with weird steamtech that I don't think ever actually happened, the far-flung future, and World War II.