Good Night, Sleep Tight!
It’s surprising what reading the back of a Horlicks jar can teach you…it says that in Shakespeare’s day, as mattresses were fastened on with ropes, they had to be tightened. Hence the phrase ‘Good Night, Sleep Tight’.
We can’t let such statements pass us by, so we boldy ventured onto the interweb to see if we could verify the statement. Many sites appear to disagree with Horlicks, The Phrase Finder quotes the following as a possible source:
The phrase actually isn’t very old. The first citation found is from 1866. In her diary Through Some Eventful Years, Susan Bradford Eppes included:
“All is ready and we leave as soon as breakfast is over. Goodbye little Diary. ‘Sleep tight and wake bright,’ for I will need you when I return”.
However, according to the 7 Ages of Manchester Festival 2006, the phrase does originate from Elizabethan times;
There are some common sayings we use today that have their origins in Elizabethan Times. The “sleep tight” part of “Night night, sleep tight and don’t let the bed bugs bite” refers to the fact that the base of beds were made of ropes strung together. As the nights passed those ropes would get loose and it was the servant’s job to tighten them to ensure a good night’s sleep. The bed bugs biting were a fact of Elizabethan life!
And here is a picture of a 16th century rope bed with curtains, recreated at Weald and Downland Museum (source)

If you want to make one for yourself, like the one pictured below, then have a wander over to House Greydragon.

Next time remind me not to read the back of Horlicks’ jars!
