This is very normal. My mom always told me that she would have breakdowns when she had time for it. Basically meaning that it always came for her after she got done taking care of whatever needed to be taken care of. It sounds to me like you're going through the same thing. There's been so much emotion and anxiety coming up to the moment for you that once it's done, it all comes out in a huge, raging wave. But, you should remember that everything is going to be ok. As much as it can be anyway. I know what you're dealing with can't really be "ok" but, you have a better idea of what needs to happen. The human race has this amazing ability to adapt to any situation. You will adapt and make it work for you and your partner. It may take time and it may be difficult, but it will be ok.
You've gotten this far and you've made it. You got to the doctor's appointment and made it through that. You've had to hold it together as much as possible and now that it's done, all that pent up energy has to come out. Try not to fight it. Ride the wave and let it come out. Write down all of your thoughts, feelings, scares, or whatever every time you start getting worked up. I don't know why, but venting like this really helps. You can also challenge your anxious thoughts by writing down what it is that is terrifying you at the moment (it could be the same thing every time or different things with each panic attack - it doesn't matter). Then challenge that thought until you see that it's not a danger. Ask yourself things like, What is the evidence of this being true? What is the evidence that this is not true? Have I gotten through this before? What is different this time that says I won't get through it again? Prove to yourself that your fears are irrational - by doing so, you will prove to yourself that you are stronger than you feel and you can handle anything that comes your way. The corner stone of all anxiety and panic attacks are irrational fears. Prove them wrong!
Challenge your anxious thoughts until you start feeling stronger. But, don't try to fight the feelings because you have been through A LOT and they need to come out. So, let them come out and then prove to yourself why everything is going to be ok.
Hang in there! I promise y