This is such a scary feeling, and I am sorry you are deep in it. A sudden sense of distance that seems inexplicable and hard to cross back makes me panicky too. I think this happens in all relationships- there will be a failure of feeling and then it will come back fine. Lots of times , it goes unnoticed, but perceptive or hyper vigilant people pick up on it more and feel it. I don't know what I hate more- nothing a failure of feeling in myself or noticing it toward me in someone to whom I usually feel connected. When this happened to me with T, I freaked out and you can see all the posts about it here. I don't think anyone does it on purpose, and it can pass barely noticed or snowball into a big problem.