I started to notice increased battery drain when I bought a case for my galaxy note 4. Nothing was showing up as suspicious on the battery usage. It took me a while to find the culprit. In the settings under accessibility, The "Air wake up" feature was enabled and I used it a lot. It allows you to wake the display by waving your palm. You can then see the time and notifications.
I found that my phone was constantly waking up when I had the case closed. One night, I lost 30% charge while sleeping. I now keep this function turned off and the problem has stopped.