I've been having anxiety and panic attacks on and off since I was 13 years old... with all different types of physical symptoms attached. I just came close to a panic today, in fact. I'm sure at the roots there are some psychological, spiritual, and biological dysfunctions in my body that are triggered by early experiences in Civ, but I try not to focus on that because I still have to live in this system, even if I don't fit in.
In short, I've found that there's a lot of truth to anxiety being caused by an instinctual "fight or flight" reaction that kicks off a circular brain-body feedback loop which results in a flood of stress hormones that trigger physical effects (increased heart rate, breathing, sweating, dry mouth, emptying stomach, all meant to help you survive in a dangerous situation) These physical symptoms trigger fearful thoughts, and the fear triggers more hormone release which triggers more symptoms and worse fear, and so on, and so on...... and this either keeps you with consistent low-level anxiety, or peaks with a panic attack, leaving you calmer but more tired afterwards.
Asking myself "what triggers my anxiety?" has become sort of a chicken/egg question. I've realized that sometimes the body informs the mind, sometimes the mind informs the body. Sometimes I feel tired, or I feel strange after ingesting certain foods, and the resulting feeling in my body gives me fearful thoughts which can then start the loop. Other times the anxiety seems to originate entirely in my thoughts or emotions. In reality, the mind and body are pretty much one and the same... but since our language-based culture raises us to think of them as competing (rather than cooperative) entities, I think we can make the mistake of trying to heal each one separately from the other.
Since I still experience bouts of anxiety, I'm not sure if I'm the best person to be giving self-help advice... but I have gotten through some long periods of depersonalization, and in the last 2 years I've become much better at stopping the feedback loop before it gets to the point of extreme discomfort. Through reading numerous anti-anxiety tips over the years and using trial and error, I've collected a number of different "tools" that have seemed to have worked for me in the past, and with practice I've become more effective at using them. They may not work for you, but they could be worth a shot.
The first tool I use is a type of awareness I learned from the "Alexander Technique"(This technique teaches you to "rewire" your approach to body movement one step at a time, rather than to just repeatedly move your body in ways that feel comfortable but are actually detrimental). Although I've never actually trained in this technique, reading about it taught me to be more aware of my posture and overall muscle use. One of the important lessons was to become acutely aware of muscle tensions, and try to release any tension that is unnecessary. This is often a good first line of defense for creeping anxiety, relaxing as many muscles as you can... I think it sends a message to the rest of your body that "things are okay" and if you also learn to maintain a healthy, "relaxed-but-confident" posture it can add a confidence-boosting psychological benefit.
Along with muscle tension, I also check my breathing. I've tried several different breathing techniques that involved counting during inhale, holding, and exhale... I found that these were good on occasion, but when overused they seemed to cause more tension and hyperventilating by overriding my natural, relaxed breathing pace. If you listen to a relaxed or sleeping dog or cat, they take an occasional deep breath and sigh, but the the rest of their breathing is a nearly inaudible...as a nice smooth flow in and out. In my experience, deep breathing is overemphasized as a tool for anxiety-prone people to relax, but I could be wrong (or probably doing it wrong). For now, I find it helpful to imitate the way that I think I breathe while I'm asleep, with the occasional yawn or sigh thrown in.
Much of the time, these three techniques (muscle relaxation, posture, and breathing) will help stop chemicals that feed the loop, before ever getting the chance to create anxious thoughts. If anxious thoughts or detachment are present or creeping in, however, it's helpful for me to identify them as mistaken thoughts and remember that what I'm experiencing at that moment is still very real, but it's just a chemical reaction, and I still have control over my own fate. I'll try to decide whether I'm having trouble managing my anxiety because I'm tired, or if I'm anxious because I'm restless. It could be both, but either way at this point I've acknowledged the anxiety and the presence of stress hormones , so I can immediately stop thinking about it and go for a walk or work on something until it dissipates, all the while keeping the relaxed muscles and breathing.
The last thing that I've found just about always saves the day is what Victor Frankl called "logotherapy," This therapy says that our primary motive in life as humans is a "will to meaning." It's a reminder of what's meaningful to you and for what purposes you are on this journey through life, and what exciting things lie ahead each time your spirit is renewed through new experiences and activities. This shouldn't be mistaken for the more overarching and meaningless question "what is the meaning of life?" Instead, Logotherapy emphasizes that life asks meaning of you in everyday situations and people you meet, and it is up to you to develop answers in response. I think when you are on the path of creating meaning you are less likely to be anxious, but when you do become anxious, I've found that even the smallest steps toward expressing, creating, working, or discovering can help that anxiety subside.. even if it's just a chore to get out of the way, or explaining something you're really interested in to someone.
I hope you can find something in there that helps, and I really really hope you feel better!