How to regain Enlightenment?
It sounds like you had some kind of realization! Rejoice! 

Now let it go. That's the only way to continue on the path. 

Reflect on the moments leading up to where you, "ceased being aware of signs of a heart attack" and, "felt slightly better and less like I was dying." How did those moments feel? Did they feel something like:


"I want nothing else but to," ... stop feeling this heart attack and
to stop dying.
Were you, "scared that now that I've lost" my life and, "will not get it back"?
Did it feel like those moments where you felt like you were dying "totally possessed" you?
Would you have done, "anything to get back" your life?


You say that, "my awakening appeared to me not from 'dying' but from the relief of not dying." Is this true? Are you sure? Or did you give up at some point and let go to the inevitability of your dying? Did you give up the struggle to stay alive? And then discovered you were not dying after all ... and attributed the euphoria you felt to the not dying rather than that state of having given up?

Those quotes in the list above are from how you currently describe your mental state. How does your current predicament of wanting to get back to your euphoria so much that you'd "do anything" compare to your past predicament of wanting not to die? How are they different?

I'm just a Buddhist patzer, but I hope this advice helps: analyze in detail those moments before you had this euphoric experience and analyze your moments now. And just let go of this realization you've had. Develop your wisdom and your compassion for other sentient beings. Continue on the path. Slowly, slowly.