Sometimes, if you're falling asleep after exercise, it could just be an indication that you're overtraining. If you're new to exercising, you may want to cut back on your exercise, and gradually increase your exercise over time.
I think it's great that you want to tackle so much mileage, but definitely, mileage is something you want to work towards building, especially to avoid the burn out factor.
When you do come home, turn on the lights, and be sure you're not in an environment that's too warm. Dark rooms and warm rooms are also more likely to make you want to fall asleep if you're exercising and getting home in the evening.
Do take at least 2 days off for rest days in the beginning, when you're just getting into exercise. Your body needs time to adapt to the exercise, and it needs time to heal. Don't forget- you exercise to stimulate muscle growth, which will lead to a higher metabolism, but the way you stimulate muscle growth is to tear the muscle from exercise, then allow yourself to heal the muscle tearing- and THAT is what stimulates muscle growth. If you spend all your time tearing muscle, and not enough time letting the muscle heal, you will never get the gains you want. You need that healing time!
Cut back for at least a month, and start it a little more slowly, then report back in a month and let us know how things are with you.
Koffee