unprotected nap
The act of taking a nap without setting an alarm. Usually, you take one of these when you have finished all of your work or are absolutely exhausted.
Mary: Thanks for bailing out on our Friday date, Jim!
Jim: Sorry Mary, I was so tired from work that I decided to take an unprotected nap
Jim: Sorry Mary, I was so tired from work that I decided to take an unprotected nap