I did this on Thursday (fell onto the corner of a wall with all my weight.....7 stitches), I just casually called my GF and asked her to take me to the hospital.
I don't shout, I tend to just sit down for a bit and breath lots. When I broke my collarbone I was around kids just before starting a show, they were asking me if I was ok so I had to pretend I was fine. I then went and told my friend/boss that I needed to go to the hospital.
Same when I broke my foot, just stayed calm and chatted to folk before Mark took me to hospital.