hi there, hiccoughs can be quite debilitating and I understand your problem. It can be caused due to just the irritation of your phrenic nerve due to any local cause like gastroesophageal reflux or a cyst, or just if you eat something too dry very fast. All these temporarily cause this problem but as you have mentioned that it has been 6 days there may be some underlying disorder causing electrolyte imbalance of which most common cause is kidney function derangements or metabolic disorder like diabetes. You should get yourself investigatied thoroughly to rule out any serious issue. For temperory relief you could try gagging yourself which will help or try valsalva manoever which is said to releive these symptoms. Take care.