They get old and start to burn up. It will keep getting worse. I'd fix it soon.
I just fixed my lights flickering issue last night.
My voltmeter would also jump around during the day as well.
Traced the issue to some wires coming off the battery that were rubbing on the fender by the shock tower. Every time I hit a bump they would touch the fender and draw power cause the gauge to jump and if it was night time the lights would flicker.
If you replace the switch, make sure the connnector isn't showing signs of overheating. Good idea to replace them both.