To further confuse the issue, there is an enormous variation in the amount of sleep people feel happy with.使问题更复杂的是，人们感到满意的睡眠时间千差万别。Don't skimp on sleep.不要缩短睡眠时间。People tend to need less sleep as they get older.人年纪大了，需要的睡眠时间往往会减少。The amount of sleep we need varies from person to person.我们需要的睡眠时间因人而异。