It's that old saying - if you think you're going mad, then you're not going mad. If you had psychosis/schizophrenia, there would be no question in your mind that your thoughts about reality were correct. The fact that you know something is wrong with the way you are thinking about reality, shows that your reality testing is intact. It's simply a problem with extreme anxiety, which is clearly causing you a great deal of suffering. Ask yourself what your greatest fears are. This is what is feeding your anxiety and causing you to dissociate so that you are separating yourself from your feelings. If you can't feel anymore then that is why nothing apart from your fears feel real.