you are being paid to fly a commercial plane! wake up!
Well and good if you were a little mechanical man. Fatigue can often be unavoidable, yet a dozing pilot is still regarded as unacceptable. IMHO, honesty is the best policy. If you truly cannot combat the need to sleep, get one of the flight attendants to keep an eye on the other guy while you recharge yourself. I believe at least one major airline has a written policy to this effect.