Scared of what it could be?

A while ago I was sleeping on my back with my partners head on my chest, my partner was awake. Suddenly I'm being woken up by my partner frantically punching my chest and screaming my name looking like he was about to burst out crying. When I finally got him to tell me what was wrong, he said that I had completely stopped breathing aswell as he couldn't hear or feel a heart beat.

When I was younger I had a few cardiac episodes where I had palpitations/fainting which were investigated however all that was found at the time was an irregular heartbeat that I was told wasn't dangerous but im scared that it could have manifested into something more serious. I'm just scared to find out and my partner is very worried about it too.
Scared of what it could be?
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