Probably British slang. Really drunk, or off yer face. Possible to use when tired. Synonyms include "mashed", "wasted", "caned".
1. Dodgy Dave was really spanked when he came back from that club last Thursday. I wonder how many cheeky fellas he'd necked?
2. I rode my unicycle to the sea and took a swim today. By the time I got back home (it was 30km there and back), picked up some groceries, scrubbed off the sunblock, prepared a green salad and steak dinner, and washed it down with a glass of Chianti, I was absolutely spanked.