What Causes Disorientation, Dizziness And Weight Loss In A 33 Year Old?

My son who is 33 is complaining of disorientation, dizziness, and weight loss. He is about 5 6 He weighed over 200 pounds . He went on some type of diet thing on the internet called isagenix for the past 2 months and did lose some weight. He was exercising doing kickboxing, and going to the gym. He has an anxiety problem and ADHD. He is always thinking that something is wrong with him. He was conivinced that he had GI cancer and the Gi doc cleared him. Now he thinks he has cancer again. Is there somewhere I can start to find out if he really has a medical problem. As a child he was in counseling from 4th grade to 8th grade then intermittently through high school. He took busbar for a short time which helped him. As an adult he will not go to consuling or take medications. He has a steady good job as a mechanical engineer. Any suggestionsjan