Be shitting bricks vulgar informal slang
Be intensely scared or frightened
We were all shitting bricks because a dog chased after us.
She lives alone, so she was shitting bricks when she indistinctly heard a voice of waking her up.
To try to imagine how would you feel if you were in someone's else situation
to show public complaint and dissatisfaction.
To have both positive and negative feelings at the same time and be uncertain about something.
To feel confident, relaxed, and not worried about doing or using something, or being present in a place or with a person
1. To do something that insures a specific consequence in the future, especially an unfortunate or terrible one.
2. To make someone think or feel something, generally something negative.
The verb "be" should be conjugated according to its tense.
The explanation for this slang may be based on a very funny fact that feeling scared, frightened and anxious causes constipation. So in many situations, you can't relax your asshole to take a shit because you are overwhelmed and stressed. And when you finally push it out, it feels like you've release a turd similar to a brick, and we have the phrase "be shitting bricks".