I admit that in some cases the problem origin could have been repressed, but this is not very common.
Not at all. Anxiety is hearing the boss music in a video game and not seeing any enemies. I'll often find myself so tense I'm holding my breath with no ability to rationalize why I'm in that state. It's a real bastard.
What I resent, actually, is when physicians are presented with a package of somatic symptoms and sympathetic/parasympathetic symptoms, and readily discard the somatic part in order to jump to the "panic attack" conclusion.
In my experience, with an OCD component with general anxiety, it can twist your thoughts so much that it's difficult to unpick what the root problem is, other than a general and overwhelming feeling of "Something's wrong". I've often likened it to having two threads running - one is your normal, rational thoughts, and the other is irrational/incoherent, anxiety fueled nonsense, which often overrides the first - but it took me months (if not more) to be able to articulate it in those terms and keep some semblance of a rational thought process rather than just going into a blind panic for no reason.
When it was first happening, it definitely felt like something of a physical origin, as I could feel my heart rate going up and up, my mouth going dry, and breathing wasn't easy (and you think the panic is _due_ to those symptoms). However, as I was getting very similar symptoms from trying to ignore certain recurring thoughts (just coupled with an overwhelming compulsion to do certain things in response), it pointed me at an anxiety-based cause pretty quickly. Without that side of it, I'd not sure when I'd've come to that conclusion.
I'm now more or less at the point where it's 'just' my OCD obsessions that set me off, which are at least foreseeable and thus somewhat more manageable, but I'll still occasionally have periods where all I feel is "something _very_ bad's about to happen"/"something's wrong"/"I need to be anywhere but here" for no apparent reason. The analogy in other post about hearing the boss music is apt - that's exactly how they feel. Thankfully they're not full-blown panic attacks (no shortness of breath or chest pain), but heart rate jumps ~40BPM, not having a wall behind me _really_ freaks me out, and I can't concentrate on anything else or really talk to anyone. They're short-lived (30 seconds-10 minutes), but it's a really sudden onset (it hits me like a wall) and I feel jumpy for the rest of the day.
Slowing my breathing helps - deliberately breathing in for 5s, then out for 5s, and trying to focus on that seems to shorten the duration, and in the situations where I can tell one is coming (OCD triggered - I usually feel increasingly tense rather than it being so sudden), it can sometimes prevent them. Drinking water also helps for those - my mouth going dry is one of the first physical things I notice, and that just increases the anxiety. Keeping my mouth wet for that period helps stop that feedback loop.
However I think that there could be cases where it would come from, e.g. thyroid instability. Usually nobody is monitored 24/7 on its thyroid hormone levels, etc. Could be also adrenal glands. Maybe when they are weak, or subject to autoimmune problems, their secretions can be irregular, or their reactions to stimuli can be too weak, too strong, quick or slow.
Then the subject would not be anymore resilient to normal stress. That would explain why normal stress => pathological effects on some people.
Then again the organ-level defects could be themselves a consequence of elevated stress during long periods, so one could raise the question about which is first of the egg or chicken...
Anxiety disorders are distressing and debilitating, and they lead to years of life lost to disability. Some of them have high rates of death by suicide.
Luckily, they're also very treatable. Most people experience pretty good recovery from an evidence based talking therapy. Sometimes that needs to be combined with medication, and sometimes the talking therapy needs to be repeated in a year or so.
So, hopefully, when people say "this sounds like a panic disorder" what they're really saying is "I understand the distress you're in, and here's some things that may help".
Sometimes it feels just like the "panic attack" is a wild card they default to when the investigation would be too complicated and the patients looks like anxious anyway (which is probably because the patients' body is playing castanets, who would not be scared of that? But they seem to invert cause and effect).