Nope, that's because you are hitting the chord really hard. Sag is the kind of sponginess to the attack you get on some amplifiers. The most obvious one is probably a Rectifier - its that sag that makes them sound so mean. A very tight amp, like a Mark IV, has almost no sag at all - notes hit quickly, with full force.
So I would almost say that sag and a tight attack are mutually exclusive.