What Causes Discomfort In The Lower Abdomen While Sleeping?

After going to sleep My father experiences a discomfort in his lower abdomen that requires him to sit up on the edge of the bed (because he knows it is going to get worse) for up to an hour. He also has tingling in both forearms. After about an hour of sitting up he can go back to sleep. He is 88 and his doctors have changed his diet, the times he eats, etc. and he gets no relief. This happens nearly every night and he is unable to get a good nights sleep which is effecting his overall health.