1) "Sleep Tight" refers to when beds were made by stringing up ropes to hold the mattress stuffing...Pulling the ropes tight made the bed more comfortable.. 2) With the advent of modern building codes, medical practices and such, bed bugs are not too common anymore, but there is a bug called a bed bug, which will bite a person during their sleep...A bed with a big infestation will provide the sleeper with a large collection of bites by morning. I don't believe that there is any disease factor assosicated with these bites...just bites.. . It is a wish for you to have healthy, comfortable sleep.