[CALUG] Sudden logout

[Howard]

Hi,
I have had this laptop suddenly logout or reboot while I am busy doing 
stuff. Not a lot,but some.

Last time I was going back and forth between thunderbird window and a 
Libreoffice Write window and an xterm or two looking stuff over, coping 
some here and there. Previous time was similar.

Suddenly screen is showing like at the end of the boot msg screen and 
then within 2 seconds the login screen. Much faster than a reboot so I 
think it is a logout which is happening.

How can I track down what is happening?

This is Fedora 25 on a 7yr old ASUS laptop.

Thanks, Howard();