Anxiety attacks follow anxious thinking. If you're fully relaxed, that doesn't sound like an anxiety attack unless the anxiety is chronic and deeply rooted and comes out when it comes out. A month without a panic attack is great unless the reason is that you're avoiding the things that trigger them, in which case you still have the anxiety problem, you're just dodging it. Sometimes that's the best we can do, and I don't know if that's your life, but being cured of panic attacks means solving the problem of thinking one's way into them. Not easy to do, and a month isn't very much time if it's a chronic problem. Only seeing a doctor for a very complete exam can show if you have something that is causing the breathing problem and even causing your anxiety attacks, as often a panic attack is diagnosed when it's a physiological problem, but again, for us chronic depressed people or anxiety sufferers, we can hold onto and obsess over things and the anxiety is always ready to come out. We either fix this in therapy or suppress it with relaxation techniques or medication or some other form of medication. So, did you fix your anxiety problem? Was it chronic or just something that happened and then went away? Did anything happen recently that might have been lingering in your mind? And if this is a regular problem with the breathing, have you seen a doc? Could even be an allergy problem but having had an anxiety problem, that can trigger anxiety.
People do indeed have panic attacks out of nowhere when they have the disorder. Not everyone, but some. That's what can make them so scary for some people and why treating them is important. However, not sure about your particular situation. Have you had this occur before? The DSM 5 specifies that panic attacks must be unexpected for panic disorder. I think this article is a good read for you https://www.psychologytoday.com/us/blog/matter-personality/201604/do-panic-attacks-really-come-out-the-blue
Do you feel anxious at other times in your life, by the way?
Since this happened, I think it is always best to see your doctor to make sure this is not something cardiac related. Sounds like you are young and this is doubtful but better safe than sorry to make sure. And at that time you can get your doctor's perspective on panic attacks. Let us know how it goes with your doctor or if you don't go to the doctor, how it is going in general. Okay?
The worst thing a person with anxiety can do is self diagnose. If you are worried, see a doctor. When a doctor listens to your chest, they will know if anything is wrong. Tell your doctor your concerns, they are there to help.
Though I am not a doctor, I will say that some of your symptoms I have experienced while having a panic attack. I’ve gone to the hospital thinking I’m dying when really I’m just having a panic attack. There’s no harm in getting checked out though.