Mine did something weird similar just before Xmas, when I took a left turn and accelerated into a gap in traffic. All power disappeared for a second, radio went off etc. Got home and lifted the bonnet, battery clamp had come loose and battery + terminal had momentarily contacted the side of the engine (metal sump under oil filter). Lucky.

It sounds like a 12V power issue, check battery 0V connection to the terminal on the inner guard and battery terminals themselves. Also power terminal on the alternator.

I have a 2/99 SB Barina with just over 20,000k's on the clock. It was a recent purchase from a little old lady who replaced the battery with the RACQ as it wouldn't start. It too has a problem with the alternator. When driving in the early morning with the lights on they would be on low beam and occasionally appear to come up on high beam as well as the alternator light would just start to flicker on faintly. We have a retired auto electrician in our club and he checked the alternator and it was putting out more than 17 volts periodically. Replace the alternator and the problem will go away. I think it is a delco remy. I'm in the process of ordering one on ebay but working out which one to order. Awaiting a reply after sending in the VIN. It is also down on power. I had one new in 98 and had far better acceleration than this one. Maybe it will perk up the little 1.4l power plant?
Good Luck.
Ron

I do not have enough knowledge about electronics but talking to the retired Auto Electrician he said my Barina was raising the voltage to the lights because of overcharging by the alternator. He said he always replaced them and never rebuilt any. It appeared to go up to high beam and it was a common problem back then. It was still on low beam but the alternator was putting out over 17 volts at times while he was checking it. I was at work at the time so I chatted with him after work. He said if I continued to drive it I would fry something eventually as it would stuff up the radio, lights and more. I did notice that the radio reception was crap since I bought it in late October. I thought it may have been the aerial but now I will wait and see if it improves once I have a new alternator on it. It is also down on power.
Cheers,
Ron