"I am aware, yes. Humans are fragile things, prone to many an illness and even worse, broken bones and even death. Because I am human, I am vulnerable to all of these things. This is not news to me." Castiel was confused as to why she was bringing this up, because it wasn't as if he didn't remind himself of these facts daily. It would often times lead him to missing his grace even more, beyond the fact that it had been a part of him for his entire existence and not having it was like missing a large portion of himself, something he was trying to fill with his other objectives like learning how to be human. He didn't realize the burden he was placing on her and what that asked of her, but if he were aware, he was certain he would have found some means of fending for himself more, just to ensure she didn't feel that way. He didn't want to lose Meg, not because he needed her, but because he wanted her there. Want, over need.
"I don't understand," he told her simply, a look of mild frustration coloring his features as he looked at her, trying to see what her point of bringing this up was. "Would you rather that I turn to Sam and Dean for help, in the future?" Not that he wanted to. Of course he trusted them, he knew they had more knowledge at being human, but he was uncertain of how to ask for help when he so often found himself let down by them in the past. More often than not, when he asked for help he was met with resistance and that was not something he experienced with Meg. He knew he should be looking after himself and he probably would have, if he'd known how to treat a cold in the first place. Instead, he'd turned to the network and to Meg, to help him with that because he knew that he would require that assistance to get through this.