Now You Can Help: How To Help That Loved One With Anxiety Feel Better
First things first, attitude. You cannot help them until they begin to help themselves (not a platitude, literally don't go trying to defuse a situation if they aren't ready to calm down yet). You are guiding them, not fixing them. Don't even think about fixing their problems. Your demeanor should be "this is happening and I am being supportive," not "there is a problem and I am fixing it."
Ask them to look at you to best they can. Eye contact is best, but it might be too hard. If they can't, let them know that it's okay and pick something easier, like an inanimate object comparable in size to a human (e.g., not something tiny like a pen or huge like the night sky or ocean). It should be unique, though. And it definitely shouldn't be fragile or broken. Look at it with them, but pay them the occasional glance to monitor their condition. If they just need to keep their eyes shut, let them and reassure them that's okay, too.
Step one was something called "grounding". She's in hell inside her head, and you've got to get her to focus on something real and concrete. Show her the way out of her head to a place where she can talk. I cannot emphasize enough how non-judgemental you have to be. It can be really hard for someone to make eye contact if they have anxiety. They might be genuinely not strong enough and if you try to make them, they might panic more. You'll have to learn a little from experience, but it might be better to switch steps one and two sometimes, or omit eye contact entirely. Maybe start a little bit of a conversation about the object they focus on instead of jumping straight into talking about their feelings. Get them to take in details of the world around them.
Ask them to describe what they're feeling. Ideally, only let them move up the order of preference before: if they were looking at a lamp and now they’re looking at you, that's a good sign. If they were looking at a lamp and now they’ve got their eyes shut or looking at their feet, that's bad. Don't comment on it, but make a mental note.
Next, you made her take an objective look at the real problem. When you're having an anxiety attack, the real problem is the anxiety attack. Your panic response is in a feedback loop: you're panicking because you're panicking. The thing that initially caused you to panic, if it was ever real, is no longer part of the equation. She needs to go from "I'm dying" to "I feel short of breath because I'm scared about ____." That's why we avoided asking her what was wrong. She's wasn't sure at that point, and if you asked her then she might've started panicking even more.
Now you can help. Say this person is your sister.
Make her understand that she is safe. Food, warmth, soft things, and hugs are all good things here, usually, but not for everyone. If she gets claustrophobic when she has an anxiety attack, it may be better to go outside with her. Read the situation. If she's still got a full on anxiety attack, maybe take some vital signs so you can prove to her that she is physically alive and well, but honestly if nothing has helped yet then we're leaving the realm of non medical expertise. Recognise that and take it seriously if that line is crossed.
If she's anxious about losing you, hug first. If she's anxious about trusting you, a blanket and some hot cocoa first. If she's anxious about something that doesn't involve you, it matters less. This can be hard to judge because at this point you still haven't asked her what's wrong. We're getting to that.
Now that no new fuel is being added to the fire, you put it out and/or stay with her until it burns itself out. If all else fails, there is one more thing you can try. Just talk to her. Let her know she's not necessarily expected to participate; just talk. Avoid topics that would make her more anxious, obviously, but really just having another person there can be really helpful..
In any case, don't just leave and go get things for her. Communication is key. Don't ask her if she wants something; she'll probably say no. Let her know you're planning to go get it for her and give her enough time to stop you if she doesn't want it or would rather have you stay by her.
Think of it this way: if you ask if she wants something, the status quo is you are not doing something but if she accepts the offer, she's given you a little extra burden. You don't mind or even think about it that way because you love her, but she can worry about that kind of thing when she has anxiety. If you just tell her what your plan is, the status quo is that you've already decided to do the thing, so she's less likely to stop you just because she feels like she doesn't deserve it.
Now, once she's begun to relax or volunteer the information, you can ask about what the initial problem was.
[Grounding techniques: I went over two of them. These are the two that, to me, are the easiest to walk a person through conversationally. There are lots of grounding techniques, but many of them would be rather obviously clinical to try and walk someone through, and I can't tell you how well that would be received. If you have the chance to talk seriously about anxiety with your partner, it can be good to go over some grounding techniques with them and encourage them to find what works for them. There are a couple more all over the internet with varying levels of academic rigor behind them.]