Wow, 18 hours is a long time to be putting up with hiccups. My first though is that I am concerned as to why you have these hiccups that last so long and why they seem to keep coming back. Hiccups are caused by an involuntary contraction of the diaphragm in response to some irritation. While the vast majority occur for unknown reasons, sometimes lung injury or irritating chemicals can cause them. I think the first step for you is to make sure there is nothing bad going on in your lung which is causing them. This will require a full exam by your doctor
and perhaps a chest x-ray. Once you have determined that your hiccups do not have a definable cause, then the next step is to treat them. Many people claim that drinking water, or trying to relax your diaphragm, or meditating can help hiccups. This may be true, but we don't have any evidence for it. One medication that has been proven to help is Thorazine. This is actually an old anti-psychotic medicine that we only rarely use, but can be helpful in severe hiccups. You can bring these issues up with your primary care physician
). He or she can perform a full evaluation and see if you warrant this type of treatment.