Black Mirror Season 3 was very good indeed. The scariest episode for me was the 5th, Men Against Fire where soldiers voluntarily are inserted a device in their brains that makes them see the enemy as zombie like creatures (roaches in this case) thus making them easy to kill. However the enemy was able to make a device to erase some of the effects of the one inserted in soldiers' brain and one realises, to his horror, that he had been killing human beings all this time. He actually had killed only two but it was enough that he agreed that the government remove the faulty device and insert a correct one (of course the whole process from the approval by the soldier stage is erased from the soldier's memory. All of the episodes have something to be scared but that one actually caused me to have a nightmare.