This works for me too. Working out in the morning (or whenever it is I decide to get up) _always_ gives me more energy for the day and it usually puts me in a good mood too.

I've heard many such articles stating that exercising increases energy levels. However, they never seem to specify exactly what type of exercise.

Are they always referring to cardio? I tried exercising in the morning a while back, but I was doing weights. I felt anything BUT energetic for the rest of the day ...

I usually do pull-ups, crunches on the pull-up bar, and lift weights (in the morning). I don't do cardio in the morning. The boost of energy I feel isn't apparent immediately after the workout (after all, you should have worn yourself out). The energy I feel might be from testosterone or perhaps it's just the feeling of being relaxed with your whole body kind of sore (in the good way).

For me I usually feel tired and crappy when I start going to the gym after a long break. I find that it is only after I exercise for a few weeks in a row that I start feeling good after a workout.

So my humble advice is to stick with your exercise routine for a while and see how that goes. good luck!

Edit: Corrected typo

I exercise to get better sleep and not to get more stuff done. A half hour of jogging and I'm out cold.

...only if these tasks are varied. I don't think this works if you focus only on one area of your life.

That is probably due to the increase in testosterone level.

It seems to work for women, too, for what it's worth.

Women enjoy increased testosterone levels from exercise too (although not very much compared with men).