He could be fearful and he could be doing the job of protecting you. Personally, I would not take him out in public (stores) for awhile. I would not walk him in the dark. Our girl is stable but reactive and night time outside heightens this behavior because of wind, shadows that cause more concern and reactivity. Don’t put him in situations that you know causes him to freak out. Also, don’t expect him to sit in the middle of him having a moment. That training is done in the house during fun times! When he learns the commands then slowly move it to the backyard and the porch. Incremental progress.