B737-800 Captain reported encountering wake turbulence in cruise flight at FL300 that resulted in an upset. Control was reestablished and the flight landed safely.

Narrative

Shortly after leveling off at FL300 we encountered what we assumed to be wake turbulence. The turbulence was enough to cause a sharp roll to the left with an immediate disconnect of the autopilot. The left roll was enough to trigger the bank angle warning although we are unsure of just how much bank was encountered before the aircraft recovered. The airspeed remained constant and less than 100 of altitude was gained before we were able to return to level flight. Fortunately; the seat belt sign was illuminated and no passenger or flight attendant injuries were reported. We landed normally and; although we were all but certain this was not a severe turbulence event; I contacted Maintenance Control after landing and confirmed with them that no inspection would be required since no airspeed exceedances were encountered. Unfortunately; due to the timing of this event (shortly after leveling off but almost immediately being cleared to descend via the arrival) we got too busy to query ATC about the proximity of another aircraft to our location.Cause: Not really applicable with this type of event.