Long back I had done many Vipassana courses at Igatpuri under Goenka. IT IS VERY HARD FOR ME TO BELEIVE THAT GUATAM BUDDHA SLEPT AFTER ENLIGHTMENT. In my view he rested lying down and went in awareness meditation automatically. The translators have assumed that he slept. They could never visualise no sleep state. In fact I would rather feel that Guatam Buddha was always in lucid state of sleep as you have explained. If you take a step further, you can say he was always in awareness even when he was lying down both at day time and night time. His body in old age required rest due to walking.