My Husband Is Experiencing Sudden Nausea And Feels As Though

My husband is experiencing sudden nausea and feels as though he could pass out. He has had this happen 4-5 times. He states that when it happens he smells a strange smell, such as a chemical smell. There is no chemical exposure though. It has happened as he was driving, sitting at home, at the store and at work. He is 60 years old with HTN and hypothyroid, he is on medication for both.

Any suggestions?