Thanks for your query
Your history is suggestive of some sort of postural vertigo
Since your doctors have done a complete cardoiological evaluation, i would recommend an ent specialist's opinion to rule out otological causes of dizziness
such as BPPV( Bening postural positional vertigo) otosclerosis
, menieres disease, labyrinthitis
And also i would suggest a complete neurological examination accompanied with an MRI of the brain to rule out cerebral causes of dizziness.
Hope i was of help