The Dr Hornbook of the poem was supposedly John Wilson, an apothecary Burns knew from Tarbolton. In a quack profession. In the Order of the Ferula. Of course, we imagine that the real Hornbook wasn't as diabolical as the character nor (as is usually the case) nearly as interesting. We suspect that Death's unuttered operation was successful in both cases.
Burns' classic disbelief-suspending device is drink, drank, drunk, which he also uses in "Tam O' Shanter": "the clachan yill had made me canty." To stagger like the speaker is to be a lucky fellow. His sheer, native imagination in the dark, unspooling Scottish lanes is what being a poet is about, sober or sozzled. A chat on a rock, hands clapped on knees, like friends, as strangers are when the night has ended too early.