Never sleep in your extensions! This tangles your extensions, causing damage and weakening hair. This would also be uncomfortable and could pull or damage your natural hair and the clips could dig in to your scalp.
Just take the clips out before you go to bed and start all over in the morning. Doing this will keep your clip in hair extensions looking their best meaning the sky is the limit on what you choose to do with your hair the following morning.
Even though clip ins are safe and simple, it is not suggested that you sleep in them. Breakage and damage to the hair could occur just from the natural movement of the head while resting.