Maybe he is just feeling insecure and needs your love and reassurance. I know it's frustrating sometimes, but he doesn't understand that you need space at night. You can't expect him to meet your needs, instead focus on meeting his need for extra love and security, no matter if it was caused by being sick or just realizing how great it was to be snuggle by his parents every night. To him, he just wants his parents to love him and tell him that everything is alright. Punishing him for that would be cruel! They are only small for such a short period of time, before you know it he'll be 15 and he won't even want you to kiss him goodnight.
Have you tried letting him snuggle in your bed and go to sleep there, then carrying him into his own bed and tucking him in while whispering sweet things in his ear and kissing him goodnight? If you absolutely can't have him in your bed, maybe make him a little sleeping space on the floor so that he knows he is welcome to come in and feel safe at night when he's scared. You never want to teach him that your bedroom is off limits, then he will feel like he can't come to you when he's in need...