I’ve taken him to the vet where he is now. I’m in need of a second opinion. The vet seems to be more interested in the trembling than the G.I. problems.
Based on your very limited description, I am suspicious that the GI problems are causing the trembling.
Trembling is one of the most nonspecific symptoms that an animal can exhibit. Anything that could make a person tremble or sweat might make a cat tremble. The causes of trembling range from anxiety to pain to cold to electrolyte imbalances to neuromuscular disorders to nausea and beyond. In your cat’s case, I suspect that exhaustion from struggling to defecate (to the point of collapse) is the cause of the trembling.
You mentioned that your cat has been having an especially hard time with hairballs this year. Hairballs most often are caused by gastrointestinal motility issues. I am concerned that your cat may have a condition such as megacolon (which leads to chronic intractable constipation and defecation outside of the box) or infiltrative bowel disease that is leading to vomiting and difficulty defecating. Other problems such as kidney disease, liver disease, or pancreatitis also may be involved.
I recommend that your cat undergo diagnostic testing. Blood tests, urine tests, and especially abdominal radiographs are in order. These tests hopefully will give insight into why your cat is suffering from the symptoms you describe.