Anyone can make a mistake. That is why they print on the medication bottles not to take medicine in the dark. The co-pilot did what he was trained to do. Worst case scenario, he could have put the plane on auto-pilot (and told the passengers to pray).
Man shot dead in northern Israel town of Bi'ina, police say the murder was gang related (Haaretz)
from the article: El Al pilot accidentally takes sleeping pill during flight