It does sound like stress is causing you major problems right now. The single biggest problem (as you've discovered) is that, when you're very stressed, things that aren't ingrained in your brain already just go away - you forget them, you can't use them, etc.
It sounds like you are a bit burned out right now, so I would take a bit of a break. That might be a week or a few weeks - it just depends on your general schedule, when you plan to apply, etc. But I do want you to work on some stress management during that break.
Go to this web page:
http://www.manhattangmat.com/gmat-prep- ... -annex.cfm
Scroll down towards the bottom and look for the article entitled "Stress Management on the GMAT." Read through that and see what you think might work for you. Then start practicing those techniques to see whether they actually do work for you. If you have other stresses in your life, you can also try these techniques for those other things and just see whether you're better able to manage your nerves and perform even while under stress.
I have worked with some students in the past who had extreme anxiety issues and some of them tried things like prescription medication, acupuncture, even hypnotherapy. I'm not suggesting you actually need to try any of those approaches; I just mention in case you feel you fall into the category. (Most of these people didn't have anxiety issues just with the GMAT - the problem was generally pervasive in any high-stress situation.)
So go take a break and try this stress management stuff. When you're ready to get back to it, we'll talk more then about what to do.