Diagnosed With Benign Vtach, On Beta Blocker. Having Sudden Lightheadedness, Sinking Feeling. Cause For Symptoms?

My son is 36 and healthy. He is about 6 1 and weighs around 187 lbs. He is active and lifts weights. He is a stay at home dad with two girls ages 7 and 3. He was diagnosed with benign vtach 5 years ago and has been on a beta blocker ever since. The medication has seemingly taken care of the vtach issue. It was suggested that he may eventually want to go off medication, but he feels good and hasn t wanted to take the risk. Recently he started with a lightheaded, sinking feeling that last for a second at a time. It can come on him at anytime, and can be brought on by changing the position of his head and is exasperated by loud noises. He has been to his general practitioner and had numerous tests including an ekg , neurological screening, blood tests and has had his blood pressure taken. All tests were negative. He has also been to an opthomologist and his vision shows no concerns. He has 20/20 vision. What are your thoughts and/or concerns about what could be causing these symptoms and what do you suggest as next steps? Concerned mother