The one quote that baffles me

I began reading the book I bought yesterday, Daughters of the Dragon by William Andrews and at the beginning, right in Chapter 3, I read something I can't figure out, however hard I tried to wrap my head round it, which I did try the whole day today. 

"...dreams are who you are when you’re too tired to be yourself."

What is the meaning of that? What am I when I'm too tired to be myself?

I still can't make out what's it's suppose to mean. Can you?

pearlie