asleep at the wheel

If you say that someone is asleep at the wheel, you mean that they are not sufficiently attentive, especially at a critical moment when vigilance is required.
“When the firemen arrived too late at the scene, the night watchman was accused of being asleep at the wheel.”

cat nap

If you have a short sleep during the day, you have a cat nap.
“My dad often has a cat nap on a Sunday afternoon.”

forty winks

If you have forty winks, you have a short sleep or rest, generally during the day.
“Dad likes to have forty winks after a game of golf.”

hit the hay / hit the sack

When you hit the hay (or hit the sack), you go to bed.
“The boys were so exhausted that they hit the hay as soon as they reached the campsite.”

lie in

If you lie in, you stay in bed after the normal time for getting up.
“Great! Tomorrow I’m not on duty so I can lie in!”

out like a light

If a person is out like a light, they are so tired that they fall asleep very quickly.
“As soon as his head touched the pillow, he was out like a light.”

ready to drop

Someone who is ready to drop is extremely tired and nearly too exhausted to stay standing.
“I’ve been shopping all day with Judy. I’m ready to drop!”

sleep like a log

If you sleep like a log, you sleep deeply or soundly.
“After a day at the beach, I usually sleep like a log.”

sleep on it

If you take time (until the next day) to think something over before making a decision, you sleep on it.
“I suggest you sleep on it. You can give me your decision tomorrow.”

not sleep a wink / not get a wink of sleep

If someone doesn’t get a wink of sleep, they don’t sleep at all.
“It was so noisy in the hotel, I didn’t get a wink of sleep.”

not lose (any) sleep

When something happens that in your opinion is not a cause for worry, you can say that you will not lose (any) sleep over it.
“I’ve mislaid the book but I’m not going to lose any sleep over it.”

let sleeping dogs lie

If you tell someone to let sleeping dogs lie, you are asking them not to interfere with a situation because they could cause problems.
“Look, they’ve settled their differences. It’s time to let sleeping dogs lie

sleeping partner

The term ‘sleeping partner’ refers to a person who invests in a business without taking an active part in its management, and whose association with the enterprise is not public knowledge.
“He works alone but his business is partly financed by a sleeping partner.”