Get out there and see the world. This is a warning shot that you aren't doing enough with your life. That fear you feel is telling you that you aren't finished doing what needs to be done and if you don't kick it up a notch, death is going to be terrifying.
Might want to check your blood for CK and Potassium deficiency as well. I've been misdiagnosed a couple times for 'heart attacks' when it was a serious lack of vitamin K.. have all the symptoms when they hit but none of the after effects till my wife started doing some research. Heart palpitations, blackout, major fatigue and slurred speech. You could have triggered this from too much gym time and not enough good food/vitamins. I get chest pains from time to time and when that happens I know my Glucose level and Potassium levels are down, we don't have adequate foods in China that I can eat so, frequent supplementation is required. Might want to get a blood test.
hey also think this is stress related due too work and relationship issues. Just going too have to take things slowly.
You can be under body breaking amounts of stress and not know it because you've internalized a lot of the stressors, eventually they just trigger by themselves and you feel the effects. I'm under a lot of stress at work too and I happen to get a lot of symptoms just before I get on the subway/bus to go to work. Comes with being a Type A I guess.
Have a bit of PTSD that hits when my temper flares up and I go into full on nuclear mode really fast, doesn't take much. I've smashed people into windows because of a small RUDE nudge on the shoulder on a staircase. If you find this in your current job then its definitely stress related.