病情分析：

一口气过敏英语可以说 "allergic at once" 或者更自然一点说 "have an allergic reaction all of a sudden"。

比如你吃了一种东西，马上打喷嚏、皮肤痒，就可以说：

"I suddenly felt itchy and started sneezing. I think I had an allergic reaction."

或者简单说：

"I’m allergic to that. It hit me right away."

也可以讲得更简单一点：

"That thing gave me allergies real quick."

总之，表达“一口气过敏”不需要太复杂，用简单句子说清楚就行。比如：

• I’m suddenly allergic.

• I had an instant allergic reaction.

• I got allergies right after I ate it.

英语里有很多方式可以说，关键是看你想表达得多清楚、多自然。

如果你是想写一段简单的英语小对话或者小故事，也可以这样说：

"I ate some peanuts and within seconds, my throat felt tight. I couldn’t breathe well. I was having an allergic reaction."

这样就很容易让人听懂你在说什么。

所以，不用太复杂，只要把“突然”和“过敏”这两个意思表达清楚就可以了。