your level could be fine and the oil pump still not working. if the light is coming one pray that the sensor is going bad because everytime that light comes on that means there is not enough pressure to supply the top end....IE: damage to the motor. 20 seconds is a long time with no oil on a motor.
a lot of people use too much gasket maker and **** like that rebuilding bikes and clog the oil jets. This will definatley cause it and definatley cause the motor to lock up.