My Husband Had A Dizzy Spell - He Is 70

my husband had a dizzy spell - he is 70 years old. he was working under his car and sharply turned his head and became dizzy. he waited until the dizziness stopped then sat up. he said he felt hot and rested his head for a moment - he said it lasted 2 - 4 minutes then went away. I suggested he take his blood pressure and it was 157/73 after a few minutes he took it again and it was 146/73. What could have caused this?