"You are alive!"
Surely this should be "You live!", which is perfectly correct in english. I tried "Jesteś żywy!"
"You live!" is accepted. "Jesteś żywy" would be a very literal translation, but I don't think it would be used if your presumably-dead friend suddenly starts breathing again...
However, added anyway, since technically that would be a correct translation. Just not very likely in real language.