I really wonder how our back can handle so much pressure from being in the same position for hours and hours.
This script uses Free Desktop Notification Client and should work out-of-the-box in any distro that ships with X.11 or Wayland. It runs as cron job that is scheduled via crontab.
Also, if you have paplay command available (Pulse Audio), it shall play a notification sound.
./INSTALLwget -qO- "https://raw.githubusercontent.com/cobrinhas/stand.up/master/DOWNLOAD" | bash