No sympathy necessary here--this is just in the nature of a reminder:
For the last couple of years, I've been bothered with occasional double vision. It was slight and intermittent, would go away entirely for three or four months, then return. CT scan ruled out the things you worry most about, brain tumor and the like, but nobody could pin down what it was.
It came back this summer when the weather warmed up, which cued a memory in my neurologist, and we finally ordered the right blood tests. Turns out I have myasthenia gravis, a rare (@35,000 cases in the country) neurological condition with a range of symptoms, of which mine are mild.
It will scare you to death if you Google it, but most patients with my history do pretty well--the phrase "normal life and nearly normal lifespan" comes up a lot in the literature. Some cases progress to generalized weakness, but I've shown no signs of that after almost two years (from the initial symptoms--diagnosis was a few months ago).
I retired in November (before I knew what was wrong) and planned to train for several months to ride the Pacific Coast in September. I'm still plenty strong enough to ride and, with training, to make the trip--but the double vision and ptosis (drooping eyelids) make it impossible to ride for more than a few minutes unless I hold one eye open with a finger, which is tedious (there are some options, which we're beginning to explore).
As I said, no sympathy is required: This is far from the worst thing that can happen, and I'm dealing with it. But if you've been planning a big trip, my advice is, Don't put it off. You never know.