Hi I Am Monalisa. My Husband Is Suffering From Giddiness

Hi I am Monalisa. My husband is suffering from giddiness and shaky legs since last 3 years. Thoght he will not have that everytime but will sometimes become too intense. We have got all tests done including MRI. Nothing has come in any test which really worries us now. He will feel lightheaded even while is sleeping on the bed. Tried different position but it remains same. Please advice. We have consulted all short of specialist and done with all tests.