Need advice and help for EF of 35%

I’m 63 and run everyday. Never really been sick.
My Apple Watch showed afib
Went to GP who gave me a holter for 24 hours.
It showed afib for 8 seconds.
She sent me to cardiologist who looked at report and said it’s nothing but let’s do an echo/stress test to make sure.
He did the test and it showed 35% EF
He was shocked and said let’s do another holter for 24 hours and see if missed anything,
He also booked me for a cardiac MRI next month.
He said sorry, I thought we would be done with this🙁
Everything I read is a death sentence.
I’m literally scared to death.
I can’t tell my wife and kids as I don’t want to worry them.
I work as a teacher and been in a fog for a week.
Does anyone have anything positive to say,
S as m I over acting?
I really need help.
Sorry to bother you guys.