write down the truths instead, they are there, you may just be hurting to much to think of them. Start very simple, what have you done that was real and positive. Even if its something very small and seemingly insignificant, start there, identify yourself.
I would write (just for me) this to start :
Mother, who gives her kids kisses and cuddles, makes their beds, feeds them, loves them
Reader of many books.
A friend to call when anything is needed.
Kind
Caring.
A dreamer.
Shy.
Someone who takes a interest in others.
Who loves music and art.
Who hates crowds.
Okay thats enough about me, but its an example of how u may be able to ground yourself again.