Need to work out if it is instrument or engine
INSTRUMENT
If it is the gauge does it act erratically ie jump up and then come down too quiickly for the engine temperature to change that much? Does it change when you thump the dashboard?
If it's the instrumentation then poor contacts to the connectors on the dashboard instrument cluster are a common fault. Could be water temp sender but they rarely go wrong
ENGINE
Does it smell hot? Overheating engines tend to smell. Is the heater hotter than usual? Is the rad fan kicking in sooner than usual or at all?
Can you drag the temperature down as normal by putting the heater and blower on? Could be clogged radiator.
Does it take longer than usual to warm up but then rises to higher than normal? If so then thermostat could be stuck.