Over the years, I have often debated whether the phrase is "In the morning, I'm going to sleep in." or "In the morning, I'm going to sleep out." My best guess is that it is a regional difference of convention.
Is it? Are there any real, historical or otherwise, reasons to prefer one over the other?
(It would be particularly nice, arm-chair linguistically, if it were "I will sleep out." but "I slept in.", though I quite doubt that fits anyone's usage.)