Al was spellbound into a peaceful state, lulled on silence, drunk on warmth, in a quiet room. He needed rest, yes, but it wasn't often when he got the rest from his own mind.
Then Snape stood up and drew his wand.
Snape spoke and it was all painful and damning. It was all true, and logical, and obvious. Al could not argue with any of it because he could offer no proof.
Snape could draw any conclusion formed from the worst case scenarios and Al could say nothing in his defense.
He froze with utter horror then, on the bench, but still asked, breathless, a betraying tremor in his voice. "Are you going to Obliviate me?" It's better to know ahead of time, he told himself. I don't want to forget this. Ever. But if this is how it has to be, I can do this.