The later. You just kind of know once you feel it. An overwhelming and sudden thought... "crap... this might be it!'.. the mind racing with intense anxiety/dread over what can only be described as "unfinished business". IE., "Is there anything I need to say that hasn't been said"... and intense sadness for your loved ones you might be about to leave behind... all hitting at once.Crazy! I've heard of the "impending doom" feeling I just can't imagine how that feels. Maybe you can explain that? But maybe it's something you can't explain you just know once you feel it.
Also, crazy that you could literally feel the clots passing through your heart. What the heck did that feel like
But... YMMV.