When do I feel nauseous when aroused..?

I'm a 14 year old girl. Naturally I read or watch some porn or porn-ish stuff or have fantasies, but I've noticed that when I get a spike of arousal, I also usually get a spike of nausea. Sometimes to the point where I think I'm going to throw up, and one time I had to go lay down it was so bad until it passed. I've googled it but nothing looks right...is this normal?