why is my phone turning off when left for a while?

[AC Question]

when in sleep mode, my phone shuts down when left for a while, and I have to restart it. can you please help me?

 

[anon(9983233)]

Please reference:
1) Settings > Display > Screen Timeout
2) Settings > Lock Screen

Also one might need to check the battery settings.. often when a device reached a warning zone, it automatically goes in to a power saving mode.