Hello Emily
You're so very close to the goal, so keep going. In terms of diminishing these panics and sending them packing, here are a few possible ideas:
Firstly, the nighttime sleep-related exaggerations of our minds are the ones we need to deal with the most, as they come during moments where our reason is not totally with us. When these happen, turn on the light and let the sleep-anxieties disperse. Even if your sleep is disrupted for some weeks or months, it's better than spending whole nights driving yourself a little nuts.
Secondly, I have found that the best way to deal with panics and other things is to confront the root of them. To be honest, I don't really agree with your statement that "anxiety is a common symptom of going through life being trans". It is something we can defeat with the appropriate coping mechanisms. What is making you anxious? I'll hazard a guess that it's a combination of work, family, prospective future partners, passing, and money to fund your transition. All valid things to provoke distress.
Take each of the ones that are weighing on you, and make a short list, on paper, of the parts of each which are in your control, and the parts which are not. Try as best as you can to quantify the severity of each one, and identify what you may need to do to influence all the parts in your favour. When I say "all", I mean that many things supposedly out of your control are not quite out of your control. For example, you might be scared about how your work will react, but if you're damn good at your job, you can influence this in your favour.
If you are worried about things like whether HRT will turn you into Claudia Schiffer, then you are worring about something totally outside your control, and my advice is to make peace, brutally if necessary, with possible practical realities. For example, in my case, due to my age I pretty much resigned myself in advance to very limited physical feminisation, and I was proven mostly correct. But while I see girls on this site obsessing about breast growth (to use a common example), it's a fixable problem with implants. It's not ideal, but it's solvable, and doesn't make me any less of a woman.
I'm not saying that you can deal rationally with the panic attacks, but it is possible. When one of them hits you, stop, and say to yourself "wait - I've already got a good plan for this one." And if necessary, go look at your list, to prove to your subconscious that you've dealt with it.
Hugs
Julia