On a long night drive you realise you cannot remember the last several kilometres, and a moment ago you went through a set of lights without registering what colour they were. What has the Handbook just described?

Correct answer: C. Warning signs of drowsy driving — pull off the road and park somewhere safe and secure

You are falling asleep. Both of those are on the Handbook's list of warning signs of drowsy driving, which runs: difficulty keeping your eyes open, your head tilting forward, your mind wandering and concentration lapsing, frequent yawning, not being able to recall the last few kilometres, missing traffic signals, your vehicle drifting into the next lane, and drifting off the road. The last two are the ones that end badly, and the earlier ones are the warning you get first. The Handbook's response is not to open a window or turn the radio up: "pull off the road and park your vehicle in a safe, secure place." Nothing short of stopping addresses the cause.

Source: MTO Driver's Handbook: Official MTO Driver's Handbook — Dealing with particular situations, Drowsy driving warning signs