Unfortunately, “I don’t know” is never a popular answer to give or to receive. I did just read an Article about a guy who had hiccups continuously for 3 years and after essentially no answers and searching for 3 years. A doctor in Japan found a small benign tumor in his brain stem that was not found on CT scan in the US. The nuerosurgeon who did his surgery in London said that if it is continuous it is in the stomach or in the brain. If it isn’t in the stomach, get the MRI. I have hiccups a LOT. But not continuously, I have had this for years, many times a day and night but it rarely goes on and on for days.