Help, cruciate ligament surgery

Dog had surgery on cruciate ligament today, in the afternoon. We picked him up 6pm and he came out of the vets on 3 of his own 4 feet. Lifted him into the car and after a few minutes he slouched down and fell asleep, all pretty normal.
When we got home we struggled to wake him and he was unable to support himself at all, not even sitting while I got my keys out. I carried him in and put him on his bed, he fell deep asleep again.
It's now 1.30am so 7 hours since we got home and at least 11 hours since he last had a widdle. Vet gave instructions to restart metacam i the morning and his paracetamol and gabapentin tonight - needless to say he has refused a drink and had no food and therefore no painkillers tonight. He looks about every half hour to check I'm here and goes back to sleep, with a groan. Clearly in pain.
The last thing I need is to waft food under his nose, for him to take it and then upchuck it, as usually happens when they eat before they are ready. But I've got no other way to get painkillers inside him!!!
It sounds like this isn't what the vet expected for tonight but does anyone have any experience of an animal still comatose 12 hours post surgery? Obviously I'm not going to bed tonight and if there's no change I'll be on the phone to the vet as soon as they open. Just hoping for any reassurance.

 

Around 4.30 I managed to get him to have his half a paracetamol, then the gabapentin, then go out for a pee. Still refused to drink until his daddy got up but the little so-and-so ... "I'm so sore and sleepy, I'm dying, I can't drink a thing ..." I didn't even leave the room just put my arm around the cat and the dog was on the sofa!!! So now the airer is on hand for any time I need to go put the kettle on or anything else. Still very sleepy but now he's on his pain killing programme I'm happy. Going forward we do have a secure enclosure, it's just for the first night as he couldn't get into his shelter-bed by himself.

 

Thank you, I have long used tuna spring water to make cats drink and he loves it too, didn't occur to me but I do have a tin in the cupboard. Like the tip about keeping some ice cubes of it too.

I have several Metacam syringes, plenty for a dribble, good thinking.

He is a lot brighter, he's had some breakfast and is more relaxed sleeping at the moment. It really takes it out of him going out to the loo so in a way that's good to make sure he gets plenty of sleep.

Thanks for your kind wishes, it is a long term project. I don't expect to be back to an hour daily walk much before the end of this year and the bal might be a thing of the past as that's the worst and up to two thirds of dogs who have this then have the other cruciate go in 12-18 months. that's a scary number.