I thought I would die this morning

I got up to go to the bathroom at 5:30 this morning.
I did the fluid exchange and got back into bed.
As I started to settle in, I noticed my watch was beeping.
I watched at the heart monitor jumped by 10’s until it read 160. I was very close to passing out, watching in credulity, all next to my sleeping husband.
I started meditative breathing and woke him to call an ambulance.
I went in and out of tachycardia for several hours, and the ER said it was almost certainly due to a potassium deficiency.
I thought I might die, was watching and feeling myself die, and the main thing I felt was disbelief.
How could I possibly die in my bed, awake, right now?
It didn’t seem possible.