If it is a one-person chamber, it is merely a large tube sitting in a horizontal position. If you are claustrophobic, this will not work for you.
You will wear either an O2 mask or clear hood, probably the former. You breathe O2, but the chamber is pressurized with air.
You will have to clear your ears continuously, and rapidly as the chamber "travels" or changes pressure. As a diver, you should be able to do this with relative ease.
As the operator fills or pressurizes the tube, it will get hot. As gas is vented to reduce pressure, it will get cold. It is also noisy.
Depending upon length of time for the treatment, it will be very boring. Other than that, no big deal.
Some chambers are set up so that you can hear music, or look through a port at a television screen outside. If the lighting is okay, you can read a book.
A little discomfort, a little noise, a lot boring, that about sums it up! Hope it helps. O2 under pressure is good for a whole lot of what ails us!