My 21 Year Old Daughter Constantly Have Seizures, Chest Pain,

my 21 year old daughter constantly have seizures, chest pain, shortness of breath, passing out, headaches and general body pain. all types of exams have been done, MRI of the brain, lungs exams, heart , has seen a neurologist but nothing has been found. all exams say she is fine.
At times she will have loss of memory . What can be the problem