What is a Pillow Book?

I know what they are, but only because I used one as the reason a model was talking naughty pictures in my ebook, "The Painted Lady".  Actually, I first read about them in a Johanna Lindsey romance, although I can't remember which one.  I really need to reread her Malory backlist - I'm sure it's one of those randy guys - to find that book!

However, in the Encyclopedia of the Exquisite, a pillowbook is descibed as "A diary, or book of musings, kept under the pillow."  The Pillowbook of Sei Shonagon, a lady-in-waiting to Japan's Empress Sadako, was a few lines written about the day before she fell asleep kind of book.  Apparently it offers great insight into the era [965-1020] in which she lived.

There were lists included in her pillowbook such as "Squalid Things", "Vexing Things", "Hateful Things", but I laughed at the "Embarassing Things" where she added an oafish lover:

"Lying awake at night, one says something to one's companion, who simply goes on sleeping."

At least she doesn't complain about their snoring.