Green’s Dictionary of Slang

exhausted, extremely tired.

1974		q. in Partridge DSUE (8 edn) 215/2: Christmas crackered for knackered (physically or mentally) exhausted.
2013		Twitter 8 July 🌐 Had a lovely day thinking of retiring its much more fun being a nanny can't move Christmas crackered.
2020		Twitter 25 Dec. 🌐 Off to bedz soon, I'm Christmas Crackered.