I don't think you're dying, either. You're having anxiety attacks. Those cause people to think they're dying instead of actually killing you.

Seriously, people can get anxiety disorders at any time, even if they haven't had them before. Stinky's question about whether you've been smoking more sativas than before is a good one because sativas, while they tend to deliver more of the upbeat, energetic, euphoric highs, also can cause more anxiety. Indicas are more relaxing and sedating/body-stoning.

Unfortunately, from what I've been reading most recently, it's the THC that not only produces much of the psycho-effective response that everyone associates with being high, it's also the chemical that, in vulnerable users, can bring on the anxious, jittery feeling. In a small percentage of the population, it's the chemical (they've found this out with testing) that can cause delusions and psychosis. CBD, the other main psychoactive chemical in weed, tends to be the component that chills and relaxes people.

Try taking a weed break and see if your anxiety gets better. If it does, you'll know that's what was aggravating it. Anxiety disorders are often helped by traditional medicines, so it would probably be worth going to see your doctor.