My wife just felt a fist sized ball in her chest,it rolled over and went away.At the moment she has the flu and acute bronchitis

You aren't quite clear. Do you mean she 'felt' like she had a fist sized ball in her chest? It rolled over?

Acute bronchitis is very serious; her lungs must be in bad shape, therefore the odd sensation.

Was there a actual "knot" a real ball or did it just feel like it was.

Is he under doctor care for her illness ?