What Causes Dizziness And Pressure To Back Of Neck And Head?

Dr i had a double hernia operation on the 9th of februry last. 8 days after i colapsed after a dizzi spell. Since then i spoke to a practioner who have been checking my blood pressure, my pressure has been ok for my age which is 75. But i am still light headed , but i feel pressure to the back of my neck and head. my concentration is not so good , In general and feeling tired most of the day. Please advice me. Thank you.