Leave all the lights on and crawl in bed and with her and hold her till she falls asleep. both of you under the covers. She will feel more secure with the weight on her.
also try leaving the lights on and crawling under the bed and coloring with her. Make it a game. Make it like camping. The more closed in she is with you the safer she will feel. and coloring will take her attention off of it. best of luck honey.
Comfort her and be there for her. Tell her words of solace, make her something to eat, bake her something, take her for a drive or something.
ask her to explain what she is afraid of...she is 12, not 2. speak to her like you would a teenager, not a child. Panic attacks have some origin. she was not born with them. try to find out what started it.
give her a sleeping pill
Give music a try. It might calm her. If it's not working, you can also sing along. Watch a fun movie together in bed. Don't leave her alone tonight simply because without mom there, everything's different and that will just exacerbate the problem.
good question. try to know the origin. observe her, give optimistic views, tame her brave, encourage her even if she is wrong. gradually she will improve. probably she experienced worst in her childhood.
ask her what she has done in the past... redirect.
Looks like you're in for an all-nighter
you're in trouble