Blowjob

Okay Ladies,
Few days ago I gave my boyfriend head I usually don't like doing this but were Almost 3 years so I'm letting my self go for him. But anyways, when I was giving him head he tried to deep throat me and I threw up !!! Lmaoooo Omg. We could not stop laughing but at the same time it was nasty of course. Has this happen to anyone else lol? Does any one has any tips on how to prevent this ? Lol