Kitten's First Shot- reaction!

So I got my 12 week old Himilayan to the vet today for a check up and his first shots. i was told by the breeder to wait even longer since they are so sensitive to shots and will stop eating. But with everyone else's advice i decided to do it at 12 weeks. He obviousely screamed when he got the shot and was really uphappy being in the car. He even ate when we got home but since then he's been sleeping. (5 hours or so) it's this deep sleep, looks like rem sleep. He wont even wake when i pet him. He'll open one eye and look at me and go right back to sleep. I guess I was expecting it, i was even told it will probably happen for a day or so but I'd just like to hear other people's experience with this. I guess I just want to hear that he'll be ok. My kitty just doesnt seem deal with stress very well. since he stopped eating once when i brought him home for a few days and i had to take him to the emergency room. He did recover from that. I just hope it doesnt happen again because of this. I hate putting him through all this.

Harvey is very sensitive to shots. He'll be out like a light for at least 24hours after. I remember when he got his first round of kitten shots I'd check him every couple of minutes to make sure he was still breathing, . The day after he's still a bit drowsy, but starts to come around. I noticed that with his other round of shots, the lethargy wasn't as bad. I did switch vets and they had a different brand and diff formulas of vaccinations. Not sure if that made a difference or if his body was more "prepared" for it. See how it goes tomorrow. If he's still incredibly lethargic, might give the vet a call.