Couple of years ago i had an accident when a pretty big person fell on my neck in the pool.x-rays showed nothing. can that injury be causing dizziness?

Depends: Tough question to answer in 400 characters but if you suffered what we would consider an injury to the brain itself such as a concussion or if stretch receptors in your neck were unduly affected because of the accident, etc. then, maybe your symptoms are related. However, the more likely possibility is that something else is causing the problem. You should talk to a doctor who can examine you.