Hello~ I am sorry you are having these issues. I hate to say this, but it does, indeed, sound like anxiety. I have issues with anxiety and I have experienced the same symptoms you have mentioned. I know how real they can feel, but I noticed the more I dwelled on them the worse they got. That tight feeling can be due to tight muscles from being so anxious and subconsciously holding your body tensely, same with the breathing issue, again, I have had both.
There is a good book by Dr Claire Weeks called "Hope and Help For your Nerves" you can get it at Amazon, it has helped me immensely, in fact, I had to purchase another copy as I wore my first one out from reading so much and all the underlining I did.
I hope you feel better soon. Feeling like this is no fun.
Малосольная семга очень помогает на завтрак.