The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

...but there is a reasonable explanation.
While I slept in my SLEEPER car...
The Big Bang Theory Season 8, Episode 1

You're a good SLEEPER.
The Big Bang Theory Season 6, Episode 8

- Not even a cozy SLEEPER car--
- Stop talking about trains!
The Big Bang Theory Season 10, Episode 11