Aggregate Values from Different Fields

Suppose I have the following fields in different do, cuments / log events:

mydomain.mylevel1.counter: 1
mydomain.mylevel2.counter: 2
mydomain.mylevel3.counter: 4

How could I treat all 3 fields as the same field? and get a values of 7 ?

You can try using the "sum" aggregation in Visualize... what exactly are you after?