Although it does help a bit, it doesn't really contain concrete enough to help a diagnosis. It could be one of a million things.
When you say you felt the loss of power, was it jerking like a misfire, or just didn't rev, or revved but didn't move?
At idle how much do the revs fluctuate?
As you say the car is new to you, the first things to do are:
a) Give it a service and clean the throttle body.
b) Scan the car for codes.
Sorry it's not very clear as I'm not that mechanically minded I've just brought the car and a few days later it's gone wrong hope this gives you some sort of idea
As you have purchased a Mk4, so you soon will be. Most reliable cars in the world, after you've replaced every single component that VW designed poorly.