Maybe because you woke earlier than your phone & it's still sleeping, jk ✌🏻. It could be your battery. it drains easily. If you over charge most of the time, it could damage your battery. If you have a lot of apps running in the background, they could drain your battery. There could be other reasons as well that I don't know. But if you couldn't figure it out then the only thing to do is have it check at the service center 🤷🏻♀️
Battery can be an issue and the battery percentage may vary according to the usage (internet, call, video playback, etc..). However, if you feel that the device battery drains quickly when no function is used, please send the device to one of the service centres to discover and fix the problem. www.samsung.com/sa/support/servicelocation/
