i can puke att will and with out a gag reflex

i have had the ability ever scense i can remember to throw up anything in my stomach without using fingers or having a gag reflex. i can also throwup like anybody els with a gag reflex. its like i have controll over some muscles in my stomach area that allowes me to controll things there. 

so how common is that ? and im i doing any damage to my body by doing this ?