Christine,
now I have done 3 of these things. The novelty has worn off. It takes about 3h (2.5h in the tube) and then there is the travel time. So half your day is shot.
It is however not a big deal at all. It feels like diving actually. (minus the water an all the interesting stuff). Basically what you have to do is equalize your ears until the pressure is stable. I find myself doing that a lot more than when you actually dive. Once you are at pressure you just wait and watch TV or sleep. (no books allowed, they are flammable). I have started to catch up on my sleep, although a bed is a lot more comfortable it can be done. They WILL wake you up 2 times for an "air" break. During this break you breath regular air as opposed to pure oxygen. So far I have not detected any vision changes.
There really is nothing to this... if anything you are more rested afterwards.

Markus