Since basically recommends 8 hours per day, and during the day you're expected to keep the body and brain active. Exercise your body in the morning by 6:30am  -8 o'clock and evening by 4pm - 6pm. Now you're also expected to sleep during the day towards noon time the your brain cells in functioning proper at least 2hours or more then at 4hours or more. With this you're sure being sound in thinking but confusion or short memories can only be as the result of lack of sleep. It can psychological state or passive events.