My iMac (2014) running OS X 10.11.3 goes to sleep every now and then several times a day while I am using it.
I do not lose any work, but it is very annoying. I do not have any hot-corners for sleep, or Energy Saver settings that cause the behavior.
After monitoring my machine using Terminal:
pmset -g pslo 2016-03-08 17:52:48 -0600 IORegisterForSystemPower: ...Sleeping...
When the event happens, I checked out the logs:
Console.app > System Log Queries > All Messages
3/8/16 5:52:48.206 PM CommCenter: Telling CSI to go low power.
Why is CommCenter telling CSI to go to low power while I am actively using my iMac?