What is going on with me? Please help?

Why do I see numbers and letters when I play music?

Whenever I play music.. red numbers float on the sheet music. I've played the violin since 6 years. I recently took note of this because my dad filmed me during my orchestra concert and I noticed that I wasn't looking at the music for a majority of the concert. Also, one time I had an old folk song stuck in my head so I closed my eyes and sung the piece in my head ..and while I did that letters appeared in my mind and I was able to figure out the song by ear. I'm not sure if everyone can do this or if I'm just an "oddball" lol. Why do I see numbers and letters when I play music? I'm 18 so I'm not sure whether I should get this check out or if it's normal