This is just my experience, I'm sure others with anxiety have had no problems whatsoever.
During the first week of ffs recovery my anxiety got a lot worse. I had two panicky/fainting episodes in the shower on day 4 and 6 and one when my surgeon came to change the dressing on day 2. I also had a major panic attack on the first night when I was doped up to my eyeballs on painkillers. I think for me the painkillers and stuff made matters worse, I started panicking because I couldn't think straight and didn't really know where I was or what was going on. I also had numerous other small anxiety attacks, but not to the point where I couldn't breathe. My partner said that valium really helped to calm me down, but after taking a tablet and waking up but not being able to move (really really scary!) I decided that valium and I didn't really agree with each other.
Having my mum, sister, aunt and girlfriend with me helped a lot, I had one of them sitting with me almost constantly from when I came out of surgery till about day 6. My sister also gave me a teddy bear to cuddle, it seems kinda childish but being able to hold on to something also helped keep me calm.