You're not being silly at all. Hmm, I have not had this experience, but I would be very worried too. Can you call the vet back and express your concerns, mention that you just want to make sure that the lack of water is not a concern for them and do they think you should force some water into Midnight. The vets are used to concerned parents, so I'm sure they'll be happy to help. Oh good luck, I do hope Midnight's lack of energy and eating is just a side effect of her vet visit and not an illness or anything. Here come some prayers your way.

BTW I love your new siggy.