I've been surviving on 6-7 hours of sleep my whole adult life. I always had to be at work, teaching, by 7:30 and usually got up at 5-5:30 AM, sometimes at 4:30. For five years I taught an aerobics class at 5 AM.
Now that I am not working, I find I naturally sleep until 6, sometimes to 7. In the summer, when it is light out, I do still get up at 5. But, I feel so much better! I never realized how sleep deprived I was, even though I go to bed early (9-10). I was fueling myself with caffeine, which was actually raising my blood pressure. I still drink coffee, but not at the same level.
Hard exercise makes me much more tired, the older I get. And like Veronica said, weight training, affects me more than riding.