I Have Had Open Heart Surgery Tetralogy Falot When I

I have had open heart surgery tetralogy falot when I was 3 and a half. They said I may need more surgeries down the line. I am 30 years old and just had that one major heart surgery. I also had throat and ear surgery by the time I was 6. The last couple of years I have had moderate-severe light headed problems. It's getting to the point that it interferes with my work and personal life. I also was told I have sleep apnea and have poor posture so the two could be related. I have known about the sleep apnea for awhile though and it's just been the last couple of years. What could be the causes of lightheadedness? It also hurts some times when the symptoms occur and I have lost my balance a couple times recently due to the symptoms. Sincerely, a concerned patient.