I went through out of the blue, it came on and lasted for two years. I'm the most calm, can face anything kind of guy and bam, I was struck with severe anxiety, panic attacks and the works about ten years ago. I thought my life was over and going to die. It was caused by depression from living in a Northern part of the world where there was no sunlight all day during the winter. I became chemically imbalanced and struggled to get through any day.
You are likely depressed, and need to treat this to make it go away. For me, moving to a sunny area and extreme lifestyle changes made it gone and gone for good. I never get anxiety anymore. During that two years, it got so bad, I couldn't even leave the house. Now I'll hike a remote mountain in the middle of nowhere and not feel an ounce of anxiety, and am not afraid to do anything.
You need to get your psyche brain chemicals in balance. This is what causes it. And you'll think you're life is over and going insane, but you're not. It's chemicals in your brain.