You probably felt an anxiety attack similar to a panic attack in symptoms but a panic attack is more severe (usually) and usually they aren’t specifically triggered by a stresser. An anxiety attack is triggered by a specific trigger/stressor (your fear of death). Both are very terrifying and have intense physical reactions but an anxiety attack will go away once you deal with the specific thing triggering you, which would be to stop worry about death which is hard but once your brain lets the fear of death lessen a bit you start coming down from that anxiety. I’ve suffered from both and I used to think they were the same thing but after having multiple panic attacks I can tell you that I’d much rather have an anxiety attack because at least then I feel like I can fix a problem or walk away and hide, with a panic attack I dissociate from my reality and believe I am literally dying. I realized the biggest difference was that with an anxiety attack I felt like I was dying and everything was falling apart. With a panic attack I truly believe that I am dying and I’m terrified with no clear way of getting out of that hole.