Hey, buddy. I've got two years on you, and there was a time when I went through quite a bit of the same stuff that you did. One possibility you might want to take a look at is Celiac Sprue. Google that one once and see what you think.
I'm not a medical doctor, so don't take anything I have to say here as medical advise, either, btw.
Bottomline is that whether it's MSG, gliadin (Celiac) (Which is 45% glutamic acid), or caffeine itself (Stimulates brain, which throws off hypothalmus, pituatory, and than the rest of the glands and organs), it's all the same problem-Glutamate overstimulating the brain, which causes everything else to happen.
Another option you might have is to see an Endocrinologist to test you for cortisol and the ACTH (Adrenal insufficiency). Sadly, however, even in that case, the brain is still behind it, you know (Pituatory controls the Adrenals, for the most part).
In my case, buddy, it was fear. Nothing more, nothing less. It caused an irregular heartbeat, high blood pressure, a creatine disruption, all of it.
There are lots of good people on this site and others like it, those that will give you outstanding advise. Several did here. But be careful with some of the other advise. There are countless people running around this place telling us that the bird flu has been invented in labs, that the government is trying to find Atlantis underneath the Denver airport, and that parasites are in control of our behavior.
Ignore it. Don't fall victim to the delusion. If you do, not only will your health detoriorate ten times worse than it is now, but your neighbors might get a little freaked out, too~.
The Big Guy Upstairs has a very interesting way of showing us certain things in life, my friend. Eventually, I figured out that in my case, it was all the result of an overwhelmning fear of death. There's a little bit of that here everywhere, as a matter of fact. If that wasn't the case, nobody would be here, afterall.
But out of the struggles come proofs, those that we are given at a personal level. I went through hell and back to find that proof, but eventually I found it. And when you have to fight to find it, the Proof of Life is all the more powerful once you've gotten there. He has His way of revealing Himself to you, so long as you put your Faith in Him.
Some of my words might sound a bit generic, and that is only because the type of experience I was put through, and the reward that came from it, only a handful ever get that in life, and you're left wondering why He gave you such a big gift when you really didn't deserve it along the way.
The fear of panic/going crazy usually hits everyone in life at some point along the way. So long as your medical tests have come up negative, consider this struggle to be a gift. It might not seem like it now, but eventually it will make sense, whenever you come to find the Truth about what this is all about.
At 26, perhaps some of this has held you back in life up to this point. But whether you're 26, 28, even 35, life's just beginning for you. Once you get this figured out, you'll be given a type of peace that will let you go on and live the rest of your life without fear. And you're likely to come out ahead because of it, trust me.