When My Son Lays Down At Night To Go To

When my son lays down at night to go to sleep, sometimes he is awakened with a feeling of a bubble in his upper stomach, chest area. It is painful and he feels like he can't breath. This started happening after he had an allergic reaction to raw onions and threw up alot. It isn't constant but when it happens he isn't able to sleep. He is 37 and hasn't had much illness in his life.