This is how you make a ride 100x more difficult for no reason.
I use Saturday mornings as my day for longer rides, usually 20 miles +. So today I got up late and that limited my time to ride. So my wife gave me the approval for a 1 1/2 hour ride, she had to leave, I had to watch my son. I like to "time" myself and see how fast I can get a certain distance done, this way I can see my improvement. However at the time I was riding I knew some of the MUPs would be busy so I dropped the distance I wanted to go and went out.
Well the first half of the ride I was bogging down, HARD. I thought maybe I had a pancake too many for breakfast, so I pressed on and hit the few hills and straightaways I ride on harder. Mind you I have an organized 50 mile ride tomorrow and wanted to make sure I was loose for it, I wasn't getting that feeling. So I hit my half-way point (10 miles) and I am 10 minutes behind where I want to be, and sweating to beat the band. So I turn around and start my trek back home. Well about 2/3 of the way through my ride I feel like I can't give anymore. My legs are burning, I am running out of water, I am getting really tired, I was resigning to pushing myself until I bonked out. I am also scared that I will have to bail on my friends tomorrow since I can't even do a 20 miler, even after a 30+ last weekend.
As I am ready to call my wife to come get me (and not excited about making that call) I am thinking about why the bike seems "heavy" today. Like I was in the wrong gear, had a flat, or maybe it was the wind? Well at this point the wind was behind/to the left of me and I knew it couldn't be that. Well I had been smelling some "plastic-y" burning smell the whole time, there are a few factories that I pass that are open making plastic products, but where I was at when I smelled it, there was nothing. So as I am riding I am inspecting the derailleurs, the chain, the tires and brakes, and then finally I see it.
MY FRICKIN' REAR TIRE WAS RUBBING THE FRAME!!! 
So here I am, cussing at everything around me ready to punch a baby because I didn't check the wheel alignment before I left. So learn from my mistakes, when you are out and noticing your time/speed is lower than usual, check to make sure your tires aren't rubbing. Especially the left side of your rear tire since as you produce torque through the chain, it can move the wheel around.
Ok, don't leave me hanging feeling foolish, let's here your story.....