yes to the above.
Also, this is not something that is over in a couple of minutes. Typically this takes 2h+ in the chamber (depending on the pressure). Add to this travel time and preparation and half your day is gone for the next 6 weeks or so. If they do HBO in prep for surgery you might get HBO before and after surgery.
I cannot tell you what is feels like. The chamber I have seen is transparent (plexiglass) and looked quite roomy, but if you are claustrophobic you should address that beforehand. You can listen to music watch TV, you will not be able to read a book. I plan to sleep if my HBO is approved.....

M