Hi Lobster. I get totally intimidated and overwhelmed by my thesis on a regular basis, starting a new chapter always throws me. But look at it this way, you've slain most of the beast already so you're clearly capable, you just need to get into it. If your mind is going blank every time you sit at the keyboard, maybe try one of the following:
1-Free write about the topic in general, no correcting, no fact checking, just keep writing for 10-15 minutes and see what comes out.
2-Talk to someone about it, sometimes when you verbalise you make links and free up your brain in ways that writing just doesn't do.
3-Grab pen and paper and sketch out a skeleton of the chapter, work on this until you have it broken down enough to head back to your keyboard, picking it off one point at a time.
Not sure if any of that will help but these things sometimes get me out of my pit of despair and back into constructive activity :-)