I'll give you some advice for this particular symptom, panic attacks, and then talk about anxiety.
This is one of my answers that was rated Best, 5 stars. It has advice for slow breathing, the name of a good self-help book, and stress management advice.
https://answers.yahoo.com/question/index?qid=20180307051
If you suffer from an anxiety disorder, I can't tell you exactly what kind of treatment you need. The National Institute for Clinical Excellence, an official health agency in the UK, has stats on what's best for most patients but not you as an individual. They rank 3 treatments - 1) therapy (CBT), 2) medicine (generally antidepressant), 3) self-help based on CBT. I'll tell you about CBT and CBT self-help, but first, here are some things with very encouraging evidence.
Recently, I discovered something very interesting that people with anxiety should know about. It has to do with two things that have been mentioned here, mindfulness and controlled breathing. What I've found is how these two things come together.
I got into breathing therapy when I read The Healing Power of the Breath by psychiatrists Richard Brown and Patricia Gerbarg. What most impresses me about this book is that it recommends a 3-part approach to mental health with traditional mind-body methods. It emphasizes slow breathing and also suggests slow body movement such as tai chi exercise and meditation.
About slow body movement, for people who suffer from anxiety, rushing around when you don't have to and doing things carelessly is bad for the nerves and makes for mistakes and accidents. Carefulness is a form of mindfulness. Slow movement is your friend. It prevents serious accidents, and your actual safety is good for your peace of mind.
You can learn tai chi from one or two beginners' videos on YouTube.
It seemed to me that Brown and Gerbarg didn't "get" mindfulness. They say practice slow breathing daily and if you have time, also do tai chi or yoga, and meditate. The mindfulness-based therapy programs teach mindfulness meditation so that people can use mindfulness throughout the day, not just for a few minutes a day.
Here's the thing. Brown-Gerbarg and mindfulness-based therapy have this in common - *awareness of breath* during the day. Respond to moments of stress by taking a few slow breaths, which will bring your breathing rate down. You might say that Brown-Gerbarg is a kind of mindfulness-based therapy.
I'll show you a video in which psychiatrist Patricia Gerbarg demonstrates a slow breathing exercise. She tells the "patient" (her husband, psychiatrist Richard Brown) to breathe *gently.* The patient doesn't have to fill his lungs completely. It's a smooth transition from inhale to exhale without pauses in-between. The breathing rate is about 5 breaths a minute, which research has shown is healthy in a number of ways - hormones, blood pressure, and brain activity. It's also the rate that requires the least effort. It's natural - you were born with it.
Brown and Gerbarg, one of the research teams that have shown that slow breathing helps people with PTSD, say that 10 to 20 min of slow breathing is a good exercise, and they recommend 20 min twice a day for people suffering from anxiety. They also recommend responding to moments of stress by slowing your breathing rate. Breathing with the belly muscle is healthy - always sit so you can breathe freely and wear comfortable clothing.
Mindfulness apps like Headspace and Calm are very popular. You can watch the reviews on YouTube and decide which one you like or try the free trials of both. A guy I know uses the free Headspace trials over and over.
Or, you could use a book. The Oxford Mindfulness Center of Oxford University recommends a book with audio exercises, Mindfulness by Williams and Penman.
By the way, one of the researchers who have shown that slow breathing helps people with PTSD is psychologist Emma Seppala. She has a really good book on how to succeed with a low-stress existence - The Happiness Track.
https://www.youtube.com/watch?v=4A_yxzNGE7g
This answer talks about 3 CBT self-help treatments, under DEPRESSION TREATMENTS.
https://answers.yahoo.com/question/index?qid=20150220041901AA0o9hk