Think hard, what were you doing that may have precipitated the slowdown?
Install anything etc.
In my own (humble) experience I've found that there was usually something that caused it.
As an example, I upgraded to V7 of AVG (free) and found a slight degradation in opening
Word & Excel. Turns out that AVG was scanning the apps for viruses.
I understand that the Norton plug-in should be disabled for Word as it causes all sorts of
problems (I can't vouch for it as I don't use Norton).