Hi capa -- wow, someone like me. I guess that we're never as unique in our vices as we think.
You're going to hate me saying this (how many times have you heard it before?), but I've found the only way I can get myself going is to do one small bit. I choose a small part that I enjoy doing and/or that has a right or wrong element to it, like a chart, diagram, the references, the title page, or I set a small amount of time, say 15 minutes, to work and then somehow convince myself to do it.
Often the looming deadline would be stress enough for me to actually write the paper, but if that's past a few times and your profs are being understanding... well I'd be up the creek in that situation. It's as if something inside me wants to know how far I can push these caring people who believe I can do it before they'll give up on me. As if I actually want them to give up on me to confirm my belief that I'll never be good enough. Crazy, eh?
Setting deadlines before the actual deadlines or having someone call every day or every few hours to check on progress may help. One time, someone actually stood behind me as I worked to make sure that I didn't stop. Talk about anxiety!!!
Ultimately, I suppose, it's challenging that voice inside you that's telling you that you cannot begin. You can, you just don't want to, or are afraid to for whatever reason. You have the strength inside you to resist that tempting voice, to calm that panicked being. You wouldn't be almost finished grad school if you were unable to do the work, so pull out that strength. You know that it doesn't have to be perfect, that you just have to get something -- anything -- in so that they aren't forced to give you zero.
Actually, sorry, ultimately it's realizing that this moment you are in is only one in a lifetime of moments. If you're getting to crisis level over this, step away. It's a piece of paper. Yes, it would be good if you could just get it done now, but pay attention to the cost to yourself and your health. (Your doctor may be able to get you a break or a longer extension so that you can find your footing again.) I realize that I'm making it sound very simple when I'm sure there are so many complex issues and expectations tied to your schooling that stepping away for a bit isn't