My online friend and fellow Charcot Marie Tooth sufferer, Lenka, describes it as "hitting the wall." It's when you have pushed yourself to far, and the meager resources of your body are simply exhausted.
That's pretty much where I am now.
The family vacation continues, but my contributions to it are steadily declining. The past two days we have taken the kids to the water park at Moody Gardens. This lets the three of them (two kids and a wife) frolic in the water while I sit on rock and watch. That's about all I have left in me anyways. Even the stairs to my resort now take a special effort of will when I come back in the evening. We were considering another day at the park, but the kids came home too red this evening. We'll have to figure out something else tomorrow.
Then it will be time to head home.
I hope the weekend is long enough for me to recuperate from this.