Here are a few reasons why sleeping with noise cancelling headphones is not a good idea, They are large and bulky and if you are someone who moves around when you sleep, you can damage them. The battery power will run out since they are active for a long time. It can make your ears very hot which can be uncomfortable. Overall it depends on individual preferences. If you don’t have any problem with wearing noise cancelling headphones while sleeping, then that is okay too.