When this goes, does it do so gradually, or does it just "fail" ?

The last couple of days I seem to have lost some mid range "power". It still seems to pull like a beast from 5,000 rpm onwards, but seems flatter than it used to in the mid range. Could this be the supercharger clutch going, or could it be that I have had loads of town driving for a few days and I need to do a Throttle reset ? Also, It doesn't seem to change down so easily (less sensitive), kick down is fine.