I have this problem too. I went to the Dr. after months of nausea, dizziness, trouble breathing, weakness etc. and collapsing. He thought the herbs I was taking for depression were causing my symptoms.
After chest ex-rays and blood work, my Doc left me a message to call him. Took me a day before I got his message and the weekend before we talked. He said I had to go to the emergency room and get a saline IV. I was told if I didn't go, brain damage from swelling, coma and death could occur.
The ER Dr. told me to drink less water, eat more salt and drink sports drinks that had sodium in them.
I am still struggling with balancing my sodium and fluids. I have no insurance and haven't had more testing to see why this is happening.
Now my legs and feet swell and hurt when I first try to walk on them. Too much sodium maybe?
Sorry I can't offer you any better advice for your nana.
I think I did read something about antidepressants causing this problem.