Happenstance

My doctor had prescribed me caffeine pills. My sister, the insomniac, had sedatives. I took the wrong one by accident.

I maintain that's the reason why I fell asleep on your shoulder that night. Sorry about that, by the way.

But it was definitely not intentional in any way. Definitely, certainly not. No chance.

You liked me anyway, by pure happenstance, though. So everything was okay, regardless.