Yeah that isn't normal, you probably got some of the critical care down the wrong way.
If you are using a syringe, switch to an eyedropper. You can mix the critical care with just a little more water so it works in the eyedropper.
You have to be extremely careful with liquids to not aspirate them, and a syringe just doesn't offer the control an eyedropper does.
When administering any kind of liquid, go slow at their pace and NEVER force it. It's even more important with babies.
As far as little Hookfang, keep a close eye on him for stress marks,
black bearding, or being lethargic. Also listen for any rasping or popping in his breathing. Or any kibd of mucus. If you see any of that, get him to a vet. Otherwise keep him a little warmer at night, just in case. If a respiratory infection sets in it may take a few days for symptoms to occur so just be diligent in watching him.
Oh and if you can find plastic eyedroppers it's better, they can bite hard enough to break the glass ones.
Keep us posted on the lil guy please.