Help I have a dilemma.

I am due to get amalgams removed on the 8th and the 9th April, great but I also have an 11.5 mile Fell running race on the 11th April! Does anyone think this will be a bad idea and if so why? I had a 15 mile fell race last Sunday and my immune system dipped for a few days after, so I have made my mind up that it would be bad to have amalgam removal straight after a race.

But what about before with a day in between? I don't know?