i too struggle with this- on those days where i'm really tired i do a partial commute of 15 miles each way instead of the 21. It allows me an extra 40 minutes of sleep. the other issue i have is around 3pm I hit this wall here at work. It's like a curtain of extreme fatigue hits me- i've actually nodded off at my desk before. it takes me about an hour to fight it off and by 4 i'm ok.