Did you know that magic users sometimes could get sick from over doing their magic? Or it would make them easier to get sick?

Yeah, you didn't.

So, when you got the random call from John Constantine, a part of you was worried until you heard his rough voice coughing. "Hey, love, mind doing this bloke a favor and bringing him some cough medicine? This bloody cough has been bugging me for days now."

Yep... John Constantine was sick and was asking you to bring him medicine.