My Son In Law 32 Years Old With No Health

My son in law 32 years old with no health issues or medications has been experiencing sporadic dizziness, nausea and double vision change in position such as standing from a sitting position tend to exacerbate it physician at emergency room placed him on cephloxin two weeks Agni which he discontinued after two days on advice of physician due to suspected allergic response. He tends to be a nervous personality but has never exhibited any symptoms of anxiety disorder that I am aware of. An thoughts re: etiology?