He can wake up one day and feel fine. The next day he has no energy. He was 72 at the time. His energy level before this was high to normal. He can walk for miles and not get tired. He exercised regularly without a problem. He's not on any medication except hypertension.
My dad is now functioning at 30%. Doctors have performed all kinds of tests to no avail. We are stumped as to what could be wrong. Any suggestions?