Panic attacks are vicious. I have had panic attacks since seventh grade, and they come and go. If you know someone who has panic attacks, here are some ways that could help them get through it. Everything listed is something that has helped me in the past.
1. Help them breathe. Sit with them and, if you have their permission, hold their hands and just breathe with them. If either of you is uncomfortable with holding hands, put one hand on your chest and the other on your stomach. Fill your chest with air first, then your stomach. Breathe in through your nose, out through your mouth.
2. Talk to them. Talk slowly, and say things such as, "This will pass. You might not be okay now, but you will be okay. It's going to be okay, this will pass. You are safe." Do not say things like, "You're okay, you're overreacting. There's nothing to worry about." That, in my case, makes it so much worse.
3. Hug them, if they are wanting to be touched. Always ask permission before you touch someone, especially if they are having a panic attack.
4. Let them cry it out if they are crying, and just sit with them until it passes.
5. If necessary, get help or take them to the nearest hospital.
It will be okay.
I believe in you.