Losing my dog in the woods

I lost my dog in Cole's Woods today. She has gotten sudenly very old in the last few months, and trails behind me when we walk, until we're clearly headed back to the car, and then she trots out in front. We don't know yet why she's so old, so suddenly. Perhaps the years oaf chronic Lyme disease or the months of drugs have damaged her kidneys and joints, and aggravated her hip dysplasia. Perhasp she's just partied hard and she is done. I am trying to walk carefully through what seems to be the beginning of the end of her life. In the woods today, we walked a loop that crosses Halfway Brook, where she usually takes a dip. She didn't today -- it was raining lightly the whole walk -- but she seemed perky, so I decided to add another little loop to the walk. I turned around and headed off on another trail. As I turned, I called Cassie, and I know that she saw me. I was thinking deeply as I was walking, not paying much attention. I turned left on a shortcut to head back to the car, and walked some more. Finally, I woke up and turned around -- no Cassie. "Cassie!"I called, sure that she was just sniffing something or dawdling. No Cassie. I went back to the turn -- no Cassie. I walked back on the trail I'd followed, calling gettin gmore and more concerned -- she doesn't even have a tag. No Cassie. I went to the brook -- no Cassie. Finally, I saw her -- up the trail where we would usually have gone. She looked unconcerned. She knows I'll come for her. I know she won't always be here.