It's difficult to explain. I've done daily meditation for many years, of course, and so I know the flavor and texture of my own thoughts. When a magical attack is in process, there's a sense of pressure in directions that aren't typical of my thoughts. I can then do various things, many of them equally hard to explain -- daily meditation has lots of benefits and some of them are fairly strange. But yes, I can usually get a clear idea of what's being done, what intention is behind it, and (often) what geographical direction it's coming from.