Good luck. There is pain, but the armpit is worse than the boob and the drains are worse than the armpit. It passes. Once those drains come out, life gets better pretty quickly. I'm a great fan of all varieties of pain relief, so I'm probably not the best person to advise you on that (I'd say take everything they offer you, which is a bit naughty if you don't really need it)
It's possible you may feel ill and disoriented immediately after your surgery, that also passes. People will ask you all sorts of irritating questions and bother you at odd hours, I'd like to say passes too, but, unfortunately they won't bloody stop. It may all be necessary, but it's terribly annoying. You've come this far, you will cope.
BTW, my best advice if you are going to be in there for a couple of days is take a thermo mug and your own teabags/coffee and a couple of treats for yourself. Hot drinks in hospitals are generally shite, be prepared. Marg xxx
