What Causes Dizziness And Fatigue While Suffering From Low Blood Sodium Levels?

for six months time my blood test have shown low blood sodium 133. MY urine testing is normal. I have been tested after repated spells of thirst, light headed & lethargy. THe symptoms do improve but I can never feel colpletely well. My doctor said my sodium has been on the low side of normal or just one number below normal during the past 2 physical exams. I am 59 and otherwise always have been healthy. I do drink red wine and since this began have quit when these spells happen. I was told to also limit my water to 48 oz and drink juice or sports drinks. ANy ideas on what is wrong with me? I have been refered to an endocrinolgist Who sent me to check for autoimune issues that do not seem unlikely but I have been tested for them and am awaiting results. Thank you