This is very similar to phenomenon of Morningglory (sometimes also called Morning Wood or BEMHO- Basic Early Morning Hard On), however this term has been coined for the opposite sex: females. It is basically the erect clitoris after just waking up. For a male, this is a very hard thing to actually experience. You may have to even camp out the night before with a video camera pointed directly at the subject in order to witness this happening. But for a female...they usually know what this is describing.
I was hoping that she wouldn't see my Morningwood this morning but then I wasn't worried as much when I actually witnessed her Morninghood.