A lot of phrases have begun to cross over from one country to the other. For example, the word nap—meaning "short sleep outside of one's normal bedtime hours"—has recently enjoyed increased usage in the UK, presumably due to American influence. As it happens, American usage of the word had been on the wane during the mid-nineteen-sixties; however, a sharp increase in literary instances of it since that time (and particularly since the mid-90s) has been observed.
By contrast, a similar word—kip—has fallen on hard times within American English (AmE), with comparatively few instances over the last couple of centuries. Indeed, the word snooze has itself trumped its three-letter rival throughout the 21st century. The same cannot be said of this word in British English (BrE), though both kip and snooze—perhaps as an indicator of the laid-back world in which we live—have been in wider use nonetheless.
Ngram: American English (AmE)
Ngram: British English (BrE)
Along these same lines, there is another word of interest: shuteye (as in, "David was so tired that he needed to get some shuteye"). This word—while relatively infrequent in its application either side of the Pond—has also gained further ground since the mid-90s. One wonders what was in the water during that decade.
Meanwhile, parents in the UK will often tell their children that it's time to go up the wooden hill to Bedfordshire (in other words, "it's time to go upstairs to bed"). In its exact form, the phrase is not used in the United States (largely because Bedfordshire is the name of a British county with no discernible relevance to most speakers of American English). However, it has been observed that the wooden hill portion of the phrase has been in use stateside.
Perhaps the most interesting part of the comparison, however, comes when we analyze each country's list of synonyms pertaining to the act of "being tired." Indeed, as with the act of "being drunk", this is where a good number of slang words enter the mix. For instance, British English plays host to words such as knackered (as well as its Cockney rhyming slang equivalent cream-crackered), while American English incorporates any of the following words and phrases: beat, bushed, done, fried, and pooped. It should be noted that bushed is also used in British English, though with a smaller degree of regularity. Surprisingly, the word knackered has gained some traction in American English—increasing steadily since the 1980s (presumably due to the influence of British popular culture).
What other words/phrases are there for sleep and tiredness? Are there any British or American usages you find funny? Let us know in the comments below.