I'm Having Allergic Reactions Where I Break Out In A

I'm having allergic reactions where I break out in a severe itching rash. I get nauseous and have difficulty breathing. I can't determine the cause. It almost always happens in the middle of the night after I've been asleep for a few hours. I wake up itching badly and it progresses from there to the point that I vomit and have trouble breathing for a short while. Then it slowly goes away.