What Could Dizziness, Nausea And High BP Indicate?

My friend is 71 yrs old and in good health. He has had prostate cancer and had his prostate removed a few years ago. recently he has been getting dizzy, nauseated, and his blood pressure has gone up to 170. his bloodpressure seems irratic. His doctor has put him on an additional bloodpressure med. and he passed a stress text with ease. What else could be going on?