[Koala77]

When you sign in, always check "remember me". That should stop it happening.

Another option which I find useful, is to type any long posts onto Word or another similar program, then copy and paste my work to to here.

Hope that helps.

[Chemar]

there is a default time after which the system logs you out for inactivity...detected by you clicking around. When making a long post, it sees you as "inactive" after the default. It is to protect your account

As Koala explained, checking "remember me" sets the default to staying logged in, even during inactivity, until you choose to use the log off feature.
Using "remember me" should solve your problem.

[EsthersDoll]

Awesome!! Thank you! (I think of "remember me" as a cookie thing that websites put onto your computer, so I never click on it and it didn't even occur to me to try that.)