Coke leaves quick. But not as quick as speed or pills. Did ANYONE read that link?
Your brain has measures to keep a constant blood pressure. Think about that. Stand up, faint. Wake up, stand up, faint. Wake up, stand up, faint. This doesn't happen cos of these measures.
You are making your heart work harder tho. Same as if you have a stressful job. You won't get a hole in it, unless you are very much predisposed to such a condition... or you get shot/stabbed in the heart.
Like all introduced chemicals, they alter the way your body is functioning by itself. The body does what it does for a reason, it's good like that. So even if you're sick, you're body is handling it it's own way. If you introduce chemicals, you'll certainly speed up the recovery (pun intended), but it comes with a sacrifice.
I'm no doctor, so unfortunately you can't sue me if I'm wrong, but don't take huge amounts of Sudafed more than once a week and you won't lose more than a few days off your life.