That's kind of how all of mine are, I feel like I'm having a heart attack and then I get faint and tunnel vision. Like the world is going dark. It always feels like I'm slowly slipping away into death.

I've been thoroughly checked out and there is nothing wrong with my heart. This is what I try to remember when this happens to me; "There is nothing wrong, this is just a feeling, it will pass, now breath deeply". It might set your mind at ease if you go get your heart checked out.

I hope this helps, I wish you the best in dealing with this, I know how scary it can be.