What is the best way to deal with sudden anxiety?

Thank you very much for your question. It's a very important and meaningful question as anxiety is something that we all have in our lives and it's a very difficult emotional reaction to cope with a lot of times in our lives. It's challenging even when we know exactly where it comes from, as it's a form of experiencing Fear which is such an unpleasant emotion for all of us as it's meant to be for letting us know that we are in danger, it's like a warning sign. However, it's even tougher when we don't even know where it's coming from and we feel it as a sudden situation, so we don't really know how to address the situation at all. Let me say that I am sorry that you are going through these situations lately and that your fears have been spreading and not allowing you to do what you want to do in your life. Let me also say, though, that your situation can be changed.

First of all, to address this anxiety and learn how to deal with this one and your other emotions, I would recommend listening to them and trying to explore fully where they come from. As a tip, I would try to see if there is something in my life that I don't like or that I would like to be different regarding my personal life, my studies/work, my relationship, my family and my social circle. Even when it comes suddenly, anxiety tends to be something that is spreading from other situations in our lives. 

The other thing I would recommend is trying to see fear and anxiety as just warnings, as I said before. When we assess the situation rationally and see that there is nothing to be afraid of, then we know that we can continue doing the things that we want to do, as the emotions can not do anything against us, we absolutely have the whole power to face the situation and experience those emotions without avoiding or reacting to them, only acknowledging them as part of us. To do this, I would try approaching little by little with some mindfulness exercises and some work with emotions. 

I truly wish you the best and I am sure you will be able to learn how to deal with anxiety in a more useful way for you.