Aww...poor Duke. I know you will be a nervous wreck tomorrow, but he'll be back to his normal self in no time. The last male I had neutered was pretty groggy afterwards. I would just monitor him closely to make sure he isn't licking...I'm sure he'll have on a collar to prevent that, but you'll have to take it off for him to eat and drink, so watch him closely.
Here's wishing him a speedy recovery.
