session screw up - any experience/hints for me?

i am saving data in the session lets say every page relates to specific session data, like: page 1 sets sess_x=1, page 2 sets sess_x=2 but if i use the history.back or the browsers back-button i can go from page 2 back to page 1 WITHOUT updating the session so what i finally have is "page 2 where sess_x=1" and that screws up the logic at some point, since the session could not be updated because the page the user sees came from the browser cache, which didnt necessitate an interaction with the server, so the server "thinks" that the user sees another page how can i handle this stuff? or prevent it from happening? or is my way of session handling weird? thanks in advance Wolfram