I don’t think it’s going to sleep. The computer is most likely going into a power saving feature because there has been no form of interaction (mouse, keyboard,track pad). IF you click on you battery icon in the task bar you can adjust the power settings and what is done. I believe it dims the screen after 5 minutes by default. You may want to change them to longer periods. You can also have separate setting if you are on battery or plugged in. You can even have it shut down if the battery is below a certain threshold.