Google "Liver Failure Support Group #7410.2". It is the best liver disease forum on the net. It has lots of people dealing with what your dad is going through and can provide answers to ALL your questions. The moderator imkindly is the next best thing to a liver surgeon.
He has been hospitalized for HE before, thats not it this time. Hes been on a restricted diet for a while. It seems to be something different this time. we just dont know what.
Also, concerning his possible HE you should ask your doctor about the need of reducing the content of animal protein in his diet.
Is he on a restricted liquid intake? He could be lacking calcium, potassium, magnesium or some vitamins.
Fruits like bananas and mangoes or sport drinks like gatorade might help. Clear it with his doctor first, because if he has ascites you got to be careful in regards to how much liquid and sodium he's having.
Also, he seems to be presenting symptoms of hepatic encephalopathy, I think you should inform his doctor and see what can be done about it, either do put him on medication or adjusting the amount he is on already.
Anyway, remember I am just a liver disease patient, so ASK HIS DOCTOR BEFORE DOING ANYTHING which might affect his treatment.
Good luck,