Energy Levels Dropping

I don't get it. Yesterday I did my typical warm-up workout consisting of 30 minutes on an elliptical trainer and another 30 minutes on my favorite precor stairmaster, which was followed by a 1.5 mile jog on the track. Not too shabby for not being in the gym for a long time.

Today I did the 30 minutes on the elliptical just fine, but within 10 minutes on the stairmaster I was tired! I wasn't exhausted from the exertion, I was simply and suddenly tired as if it was 3am. I finished my half hour, but decided against my jog (I wanted to see if I could hit 2 miles easily again).

I don't get it. I had a decent amount of sleep, but I'm feeling drained now.

Oh E. I did have a good chuck of a post per your request, but Blogger ate it! I'll recreate it later tonight or tomorrow so don't think I've forgotten about you. If anyone else has topic ideas feel free to put them in the Comments field!