Basicaly, whenever I was writing my code, I would declare a session only in "default" part of the switch statement. This ment that whenever page loaded with any data POSTED to it, the session was not declared and the variables seem to not have been saved.
The solution seems to be writing session_start() in every instance of the "switch" statement.
Doh! Didn't even notice that -- so what if you place the session_start(); call before the switch statement [preferably at the top of the PHP block, before any other PHP code]? Does that eliminate the need for the multiple session_start(); calls within the switch statement?
There's been some problem with it, but I think it's down to the fact that I was declaring session variable on the top as well, so one would have to declare them in the "default" part of the switch statement