With about 10 miles to go on my normal morning ride I began to sense that the trike was not rolling as well as usual. I have had this delusion before, and never found any real cause, just an "off day".
I completed the ride, but noticed my knees hurt a little bit more than usual. My average speed was off by a half MPH.
So I get home, and get off the trike. Oops, I have a flat rear tire. It appears I rode about 10 miles with a flat.