Wenn Du in UK unerwegs bist, versteht man Dich auch, wenn Du sagst "I was completely knackered for the rest of the day."

I think "toast" is an Americanism. For a comparably colloquial British expression, you could use "zonked". If you want something neutral, I think "useless" would do.

I wouldn't use "knackered" in this context.

Why not? Just being curious.

To me "knackered" means "exceedingly tired as a result of my own efforts".

So if you've worked all day long or ridden your bike quite hard, you'd be knackered, but not, if you have suffered something more or less passively?

Good to know.

Das ging ja schnell!

VIELEN DANK !!!

@Bacon: Yes, that is certainly how I would use the word, but it being very colloquial, there may be other opinions.

@Andrea: For your whole sentence, ...

"I was at the dentist's in the morning and thanks to the anaesthetic, I was completely zonked/useless for the rest of the day."

Note also that British and American spellings of an[a]esthetic are different!

I was totally out of it for the rest of the day