Can vertigo and dry heaves cause high blood pressure or vice versa?

My diabetic father is suffering from unexplained intermittent attacks of nausea, vertigo, and dry heaves. The episodes usually last 2-3 minutes and the dry heaves and spinning are very intense. When these attacks occur his blood pressure skyrockets to around 200/100 from normally around 120/70 on his BP med. He is unsure which is occurring first- his BP going up and causing the episodes, or the episodes causing his BP to shoot up. He has had a tilt table test, MRI and CT scan which all revealed nothing.  He has been treated for an inner ear infection but does not feel that it was helpful. While he does have congestive heart failure, he does not have any chest pain, shortness of breath, pain radiating into the arms, etc... or any signs of heart attack or stroke during these. He has experienced these attacks for about 6 years. He is a veteran and does suffer from PTSD, but does not feel that anxiety is a triggering cause. I feel he should see either a GI specialist or an ENT, or both. Any insight or feedback is appreciated.