I've noticed today that when I flick my lowbeams on, my highbeams come on instead. If I pull the switch as if to turn them on, the blue highbeam indicator light in the cluster goes on, but nothing else changes.

It never used to be like this. There is HIDs installed

 

Check the plug on the HID side and see if the wires are rusted / old . the ground for both low beam and high beam use 1 wire .