Mac High Sierra falls asleep immediately after playing youtube video

I noticed after updating to High Sierra. Immediately after playing a youtube video (sometimes 10 seconds, sometimes a few minutes), my computer logs out and goes to the screensaver. My system settings are all correct, I have my computer set to sleep after 5 mins. It seems completely random, sometimes my computer stays awake during the whole video, sometimes it logs out after a few seconds. It doesn't have to do with the duration of the video. Has anyone else had issues like this, and does anyone know of a fix?