0.5 bar would not be considered low oil pressure at idle, but another cause of a sudden change is oil pressure is a bad sending unit.
My oil pressure went to zero at idle, and I was ****ting bricks. The needle would go right back up when the car was moving, though.
It just turned out to be a bad sending unit.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".