10 year old with sever anxiety

I'm at my wit's end with my 10 year old son. He is getting anxious over the most ridiculous things for example , he had a pain in his knee (from soccer training) and diagnosed himself with a tumour .. he worked himself up so much he had a full blown panic attack and almost passed out .. another incident was he was playing with a Lazer with his friends and convinced himself he was blind after it !!! It just came in crying because he got some slime on his lip and thinks it is going to poison him !! When I comfort him he just will not listen .. he keep asking the same thing over and over and over "am I going to die now " ... My patience are gone !!