When you cannot take a decision on something right away, and need some time to think about it, you say that you need to “sleep on it.”
I haven’t been able to make up my mind about your offer. Let me sleep on it and get back to you in a few days.
“I’m not sure which car to buy.”
“Well, why don’t you sleep on it and let me know later? “
“Yes, I’ll do that.”
Don’t confuse this with ‘sleep in,’ which means to sleep for a longer time in the day than you normally would, or in other words, waking up later in the day.
Tomorrow is Sunday and I’m going to sleep in. Don’t call me before 10.
Ah! The kids are at their grandparents’ place and my husband is away too. I’m looking forward to sleeping in tomorrow and spending a leisurely day reading on bed and watching movies.