It's two steps forward and one back (okay, sometimes three back).
The key is you have had days at 99% so you know you will go back there again. Your brain is working with a deficit from the initial injury and is dealing with the loss of vestibular function left over by that. I liken it to recovering from a stroke, one part of your brain (or in this case your inner ear) is not working at full capacity, therefore the rest of the brain has to do that extra function or compensate for the loss of inner ear function. So when you go through any major stress, including a cold, the brain is taking on even more and the first thing it will give up is that added load, hence the decomp.
So bear with it, each time tends to be better and better, shorter and shorter. And each time you go through a stong period I believe we raise the bar on what we expect. If we could record what level our heads were really at I think we would find that we are actually functioning at a hight capacity that we think we are, but once you have a taste of that sweet compensation, you want more!!!
Drink water, move your body, and decomp will come! again...
Just want to also say -- as I am in the middle of a cold and feeling miserable... That our Immune Systems take a beating with this thing leaving us more susceptible to catching bugs.... I think its better to be a germaphobe while dealing with this to avoid these types of setbacks.....
I really cant tell if I'm having much more colds now than before, because colds ara quite a chronic condition in me.
I know that, closing to the 2 year mark with this, there are times that your bran can compenste quite well even for colds, so you feel like hell just for the cold alone, but not dizzy.
During my present "relapse" "decomp" or "new episode" form this year, I've been much more affected by the cold effects on my dizziness, and they sure give me hell, taking me down from a 99% much like yourself, to an awful level..., much like in the past weks.
I don't know if this thing actually makes your inmune system less efective or not, but, because of the dizzy side effects, I pay twice the attention to my colds than before, that's for sure.