"By now, I am really bricking myself. My girfriend nas no idea what Pablo might do to us if he finds us here."
Well, there is an idiom and it's not a very nice idiom but here it goes:
shit a brick (shit bricks) - to be anxious or to be scared.
I am bricking myself is about the same as I am shitting bricks.
...and that means I am very scared.
Sorry for the bluntness, in this case I wouldn't know how else to explain it.