If you haven't moved (i.e. your session key has not seen activity for about 15 minutes) the system presumes you have left, and are off-line. The system uses a cookie to log you in. If the total time on the top right of the screen does not equal wall time since you visited the site first, you're ok.
If it says something like "Total time logged in: 65 days, 12 hours and 14 minutes", boy, have you got problems.
For me (and I do spend a fair amount of time on the site) it says today, on the 15th of january: 2 days, 19 hours, and 13 minutes...
Not a lot of people can top that today, but you (with 1 day, 12 hours and 52 minutes), are getting close. You are a far more prolific poster though, with 2023 posts!
Peter