Here's the National Geographic Dog Toxicity Chart - might be useful at this chocolate-y time of year?
My dog's eaten chocolate before - he can sniff it out in handbags, embarrassingly - but touch wood, the only side effects have been less than pleasant poos. We keep everything in tins now, to be on the safe side, though.
Hi our large dog ate about a kilo of dark choc at 6 months - must be the age for it! Can you call an out of hours vet for advice? I think severity depends on quantity relative to size and cocoa content. Our dog was v v ill and vet didn't think he'd make it at one point, he saved him with pints and pints of liquid charcoal. Dog pooed bbq bricks for days! Try to get professional advice jic but sure he's not as bad as ours was. I'd assume colouring in crayon caused crazy behaviour.
My golden retriever managed to eat 200 grams of dark chocolate when he was about that age. I rang the vet and they said he would be fine - was very subdued for a few days but was fine. No manic behaviour tho'