Engine oil level low ,Add oil

[Rocky33]

Hi everyone ,interested to know if someone have had this issue before ,Yesterday i was on a motorway  , warning came on the dash board "engine oil level low add oil ,the first thing i did obviously was to check dipstick level and it showed the level was fine .I had already booked the car for oil and filter change this saturday before this warning ,last oil changed was 5K km /6 months ago.i did lot of short journeys last 2 months so decided to have it changed after 6 months as oil life  is sitting at 12 percent.after checking dipstick,i initially thought it could be the moisture in oil which might have evaporated and sensor might have acted funny but now after little online search ,i have seen that it could be a faulty sensor in oil pan ? This is the first time ever happened in 3 years ownership of this car.Do you think i should ask garage to change oil sensor ,is it expensive labour job ? I dont see any fault codes so not sure if its worth spending the extra changing the sensor if it is working fine ,i dont see any oil leaks inside or around engine bay ,so far it has happened only once ,does it point towards something serious if it is not just a sensor?  Engine is 1.7 CDTI  ,A17DTS ,Mileage 136000km Thanks Guys .