Yesterday, after my Octavia had warming up I thought I would give her an italian tune up. At about 70 miles MPH have kept higher revs through the gears I had a sudden loss of power (at about 4000 RPM) but no warning lights. I couldnt get the car to rev. On stopping and turning off the engine is seems to reset itself, but same problem.

 

This morning all is ok but Im driving normally and not reving beyond 3,000 RPM ...

 

Anyone know what may be happening?

Have it scanned - you may well have the start of sticky vane syndrome - have a read of this thread http://www.briskoda.net/forums/topic/243533-the-mr-muscle-vnt-turbo-treatment-thought-we-needed-a-guide-of-sorts/