wake up 单指从睡梦中醒来
get up 不光指醒来,还包含起床这个动作
I nearly always wake up fresh and rested.
我几乎每天醒来都精神抖擞，得到了充分休息。
They have to get up early in the morning.
他们大清早就得起床。
They knew how to get themselves up in those days.
那时候，他们懂得打扮。
