2005 BMW 320D Electrical fault causes car to cut out on mot

I have a 2005 BMW 320d M-Sport. Yesterday the engine cut-off on the motorway and all sorts of warnings came up on dash. The rev counter needle flicked back and forth violently and steering/brakes etc was very heavy - it had effectively gone dead. I came to a stop and pressed 'Stop' button took key out of ignition and then put it back in and pressed 'Start' - since then everything (driving-wise) has been fine.
So as im worried I took it to auto-electricians who cleared 3 faults, 2 of which were camshaft and crankshaft sensors. His plan is now to see if it occurs again and then identify by the faults appearing on diagnostic machine that these are actually faulty sensors as opposed to just been 'tripped' - my questions I guess are can this just happen? Will it happen again? Or is there a possibility it was a "bug in the system" and will never occur again (ive driven 35 miles since) - how much are the replacement sensors to buy? And will they clear up the problem!