Is this the only fish in the tank? If not are any others acting odd? What kind of behaviors are you noticing with the bangai? Lethargy, heavy breathing, excessive hiding, swimming into the flow of a powerhead/filter, any odd spots patches etc.? How long has the fish been on the bottom like that and how long have you had it? What and when was the last wet thing added? As stated above you do have some ammonia readings which may be what is affecting the fish, however I also want to rule out any symptoms of disease. Definitely get on the water change and also try to find the source of that ammonia spike.