I would also say that 25mg. of Metoprolol is a very low dose. I believe one of the primary uses of Diovan is for congestive heart failure. Do you know if you have this condition? Perhaps it's that, or the Diovan that's making you feel fatigued.
Metoprolol is now a second line drug for controlling blood pressure. There arenow newer drugs available that will do the job without the unwanted side effects.
I hope no one here gives you advice on going off a medication that doesn't included you discussing with your doctor.
On the general subject of Metoprolol I'll say 25 mg once a day is a very low dose and hope your get some feed back from others on side effects. It seems they vary greatly person to person. For me 50 mg a day has minimal side effects, but yes, it does cause some fatigue. I am also in permanent atrial fibrillation which may be the real issue for me. I had taken Toprolol when much younger and in normal sinus rhythm (then it too was 50mg SR) and it had no side effects that I can recall, I was still running for exercise.
You might want to discuss using a calcium channel blocker to lower blood pressure.
In all my comments are made with no knowledge of "diovan" and its side-effects.
Good luck in finding a way to keep the BP normal, that is an important issue.