Erratic speedometer

I have a 1989 Toyota Camry with a V6 engine & 210K miles. When driving at highway speeds I notice that the speedometer’s needle rapidly shaking & briskly sweeping when driving over 45 mph (i.e. I had my reading go towards 100 mph when I’m only traveling 65-70 mph while on the freeway).

What’s causing this? Last time it occured was about seven months ago, afterwards the needle stabilzed thus giving the correct reading

then it started to act up.

Could be the speedo cable is about to fail. Same thing happened to my '88 Supra for over a year, then it finally broken, leaving me with no working speedo. My local dealer had the part in stock.