A problem I can't diagnose
This morning I was about 5 miles into a ride when, I started to feel more rolling resistance than I am used to. It felt like a brake was rubbing. I stopped and checked things out. I couldn't find a problem. The wheels, cranks, and chain all spun fine with no unusual resistance. Both tires had plenty of air. I couldn't hear any unusual noises either. I tried riding again, but the problem persisted. At this point I think it might all be in my head. If it is a legitimate problem it must only happen when my weight is on the bike.
Does anyone have any suggestions? Am I just crazy?
Try taking the bike out again on a level road. When you feel the resistance stop pedaling and see if the bike coasts normally or comes to an abnormally rapid stop. That will tell you if it's a mechanical or physical problem.
One idea, check for a broken spoke. The wheel may remain true enough to turn freely unloaded but the rim may flex enough under load to rub on the brakes.
One possibility is a cracked frame. Your weight or exertion could open the crack and cause deformation of the frame. As a result, brakes could rub.