If you tend to over react, consider the possibility that it's not tendonitis.
Taper madness is illustrated in a variety of ways in the last few weeks prior to the marathon. You might find yourself driving more safely because you are running the marathon. You might feel new aches or pains in strange places that concern you because you are running the marathon. Or, better yet, you may find yourself buying things like leopard running tights that you think for sure will help get you across that finish line.
During the first part of Taper Madness you will hear about every small ache and pain and how it may be a broken leg or torn ligament or some other traumatic injury. Every twinge becomes a reason to think about postponing the marathon effort. Every sneeze, sniffle, cough or pimple becomes a life-threatening virus or infection. Tight hammies, inflamed ITB, tweaked Achilles, plantar fascitis, black toenails, bloody nipples, chafing, and this is just during breakfast.
These descriptions, especially the second one, fit pretty well with what a lot of runners go through during the taper. Phantom pains show up, things that were just a bit sore during training all of a sudden are serious issues. This is normal during the taper. If you already tend to over react, I'd consider it a real possiblity that you're just experiencing taper madness. Of course, I'd never want to rule out the possibility of this being something real because it may be and, if it is, it should be treated as appropriate. However, it wouldn't surprise me if, no matter what you do over the coming days, you forget all about the ankle by the end of the first mile on Sunday.