Pro runners, especially distance runners, apparently do this all the time. Of course, instead of going to their job between sessions they take an afternoon nap instead. But that's how they're able to rack up 150+ mile weeks. It normally takes me a full month to total that many miles, so I don't really need double days. This week was a special occasion, having missed my run several days in a row due to a number of obstacles both thrust on me and self-imposed.
The hard part, for me, is crawling out of bed early enough in the morning to get the first run in. Even just 5 miles can take me 45 minutes, so it requires some time, and I just don't wake up easily. I know this is because I also don't go to bed easily. I'm stubborn and won't lay down to sleep. But I choose to blame this on heredity: My father is notorious for having the same problem.
I've long had the idea that I should start most every day - maybe 5 times a week - with, say, a 2-mile run. Nothing flashy, nothing ambitious. Just roll out of bed, slip on my New Balances and run a mile up the road and back. It'd take me about 20 minutes door to door. It'd get my blood flowing with a gentle jolt. I could add a few more miles into my weekly total. The obstacle? Just waking up in the first place. Well, it's not like I'm slouching. I do a very respectable 40 to 50 miles a week already when I'm working up to an event. It's just a moral victory out there for me to still win. Then everyday would be a "double day".