Strange Problem After Low Back Injury

Hello, i am 26 yeas old suffering l5-s1 disc herniation from injury in gym. Yes, my fav exercise deadlift take one of my 9 lives. After 2 years with constant battle now i don’t have back pain no matter sitting, lying or straight.
My only and main issue is when i am sit. After 15min. or more start to feel dizziness in my head, don’t have back pain or other pain, just dizziness and can’t focus good what i read. Really don’t understand why this happen and how to fix it. My only problem is in lumbar region. Everything (knock on wood) is good.
I was on 2 neuro, but they only write prescriptions for pills. This problem is always happen. Please, if someone have idea what can be, help.