This is so easy to do so don't feel too bad. I'm sure we've all done it at some point, I know we have. Like Nigel says, keep a close eye on his blood sugars today, make sure he does lots of testing and keep some extra snacks and hypo treatment with him at all times. Still keep doing the Novorapid to cover meals but if he's finding his blood sugars are dropping a bit low during the day then he could reduce his Novorapid slightly with each meal, but I wouldn't not do it altogether. Keep an eye on his blood sugars for the next 24 hours after which time most of the extra levemir should have worn off out of his system.