Can you "topple" a Direction Indicator?
 

Just been to Alderney Fly-In and took part in the Navex. There was a timed start over a farm just inside the French Coast. Arrived well-early and weaved and weaved and made multiple slow orbits (in both directions) before running in to get the timed start right. Then horror - DI wasn't responding at all. Just didn't move in response to any turns, even though I had suction. Did the course flying the map (more than the compass), and the DI was U/S. Started the aircraft a day later, flew home, and it's working fine. I know you can upset an AH, but can you do the same to a DI, as its also a gyro mechanism? Should I be worried about future working of the instrument?

Did you reset the DI just prior to the start of the course ? When you push in the knob to align the DG with the mag compass you lock the mechanism. The knob is supposed to be spring loaded to the out ( free ) position but sometimes the knob won't come all the way out and the DG winds up locked and unable to turn.

I was on a nav ex while doing my ppl in a152 and noticed half way down the second leg that Di stoped moving on roll out from a turn ! Did the rest of the trip on the little bubble compass , turned out the giro in the Di packed up

Austerwobbler :)

You can certainly topple the DI doing aeros, though I would not expect this from the manoeuvres you describe, sounds more like, as mentioned earlier, the heading knob sticking.