Hey there! Glad to hear you're feeling better and it's just post-op pain you have to go through. I went for a swim in my local hotel pool for the first time today since surgery (just over 5 weeks) and even though I feel great for it, I'm tired now! You'll probably bounce back quick enough, but do give your body time to recover.
So, coasters, huh? I've avoided them since I had my shunt fitted as I'm MEGA pressure-sensitive. I was nearly re-admitted two days ago as the drop in air pressure due to rain coming in made me so bad I thought I was going through shunt failure! If you've been ok on rides before I reckon you'd still be ok. And I can't imagine a shunt coming apart on one of those things as you yourself will be pretty still. I went on one ride which spun around very fast once and I swore never to do THAT again! It was only a little kiddies ride too! I fairly had to be helped off it and all the children were staring . So I guess the only way to find out is to try a moderately tame one (if there is such a thing as a tame rollercoaster) and see how you go! Good luck! Personally I think you're mad WANTING to go on those things!