I checked the online chocolate toxicity guide - and then phoned the nearest emergency vet. After some discussions, they advised that she'd thrown up enough chocolate to take herself out of the danger zone and would probably be sick some more, have diarrhoea etc, so to keep an eye on her overnight. If I wanted to bring her in this was fine - but just to be aware the initial cost would be £200 plus !
So after clearing everything up I slept on the sofa to keep an eye on her. Thankfully she was fine - no further sickness or anything else.
It was however a sobering reminder. It was my fault - I left the chocolate in a bag on the floor with all the other shopping (I'd let her sniff it and she hadn't been interested so I assumed it was sealed enough to avoid arousing her interest), and was out long enough for her to become bored and start looking through stuff.
The knock-on was that instead of leaving at 9am the next morning to drive home I had a couple more hours sleep once the house had gone to work, then got ready and as away to leave at 1pm - only to realise I'd left the car keys in the house and put the door key through the letterbox!
So Maddie had an unexpected walk (thank god it was a nice day) as one friend works an hour and a half drive away and her husband isn't allowed a phone at his work. Eventually I got hold of someone, discovered the neighbour had a key, waited for the neighbour to get home and was finally able to drive off at 3.30pm. (I actually had a lovely drive home, not too many holdups and a lovely sunset)
Poor Maddie!