What is the difference between a loss of control and an upset?
Aircraft upset 


   is a dangerous condition in aircraft operations in
  which the flight attitude or airspeed of an aircraft is outside the
  normal bounds of operation for which it is designed. This may result
  in the loss of control (LOC) of the aircraft, and sometimes the total
  loss of the aircraft itself. 


Loss of control


   is the unintended departure of
  an aircraft from controlled flight, and is a significant factor in
  several aviation accidents worldwide and the leading cause of jet
  fatalities worldwide. Loss of control may be the result of
  mechanical failure, external disturbances, aircraft upset conditions,
  or inappropriate crew actions or responses.


TL;DR: 


Upset occurs when attitude and/or airspeed are outside of the boundaries where the aircraft is controllable.
Upset is one of many possible causes for loss of control.