If i think too much about throwing up, it will make me throw up.

if i think too much about throwing up, ill get sick, and start throwing up. when i was little it was really bad, id do it before going to bed, and especially when i go out to eat, ill just feel like i ate too much and ill start to feel sick and throw up everything i ate. any thought or sight of puke, will make me blow chunks. is this normal?