The headache leads me to believe that your problem is somewhat hydration related. Add to that the lack of energy and I begin to suspect an overall nutrition and hydration problem as well as over exertion.
We all have off days where we don't eat/drink enough and then overwork during a ride. Sometimes it's because of a lack of QUALITY sleep prior to riding or some other reason. If you add in a poor diet prior to the heavy exercise you will get the result you're seeing.
You'll probably return to normal in a couple more days. In the future you should be sure to carb load prior to long rides and be sure to hydrate well before and during the ride and don't forget to eat during the ride.