Diagnosis
That's spooky, but it's almost always a feature, not a ghost. The main culprits are HDMI-CEC (Anynet+) where a connected device wakes it, the internal "Auto Power On" schedule, or a faulty wake-from-LAN setting.
How to Fix It
Go to Settings > All Settings > General & Privacy. Turn OFF "Power On Via Mobile" and "Power On With WiFi." Next, go to Connection > External Device Manager > HDMI Settings and turn OFF "Input Signal Plus" for each HDMI port temporarily as a test. Also, disable "Auto Power On" in the same External Device Manager menu. See if the phantom boots stop.
If That Didn't Work
Check your timers. Go to Settings > All Settings > General & Privacy > System Manager > Time > Sleep Timer & Auto Off. Make sure no sleep timer is active and that "Auto Off" is set to "Off." Also, in the same System Manager menu, go to "Power and Energy Saving" and disable "Ambient Mode Detection" if it's on.
Heads Up
If you have a cable box, game console, or soundbar connected via HDMI, their CEC signals can be flaky. Try unplugging all HDMI devices one night to isolate the culprit. If the TV still turns on with everything unplugged and all settings off, a full factory reset (Settings > Support > Self Diagnosis > Reset) is the last step before a service call.