My thoughts and good wishes for what you and your son are going through. I understand that sometimes the experience of watching him go through these things is also very hard and stressful for you. I am 100% in agreement with the idea that the amount of blood drawn does have a relationship to the amount of dizziness, whooziness, light headedness, etc. I'm one of those folks (think it may be related to low blood pressure) who doesn't react well to having anything more than a few drops of blood taken out of me, and fifteen vials put me on the floor at a LabCorps facility similar to what happened to your son. I've found the people at the phlebotomy labs are usually very professional and helpful, as they have had lots of experience with drawing blood and how different people may react. I very much agree that a formal complaint to the company is appropriate here for the negative experience you had.
But though you can certainly check with an attorney, it's not going to be easy to show that your doctor was medically negligent for asking for a lot of blood to be drawn, I can see no easily visible malpractice from that angle. And you very likely would not be able to go after LabCorps legally for not having juices or crackers or for not being supportive enough or well prepared enough when they draw a large amount of blood from a frail patient and have them faint, vomit, lie on the bathroom floor, etc. Even though it sounds as though they were very unsupportive, and you feel there were definitely emotional damages from somewhere, without real physical damage due to negligence, it's going to be very difficult to pinpoint who would be at fault and sue-able here. Lasting emotional damage is very hard to prove, would possibly need to be shown by counseling and treatment by a therapist.
And it does seem that some counseling and coaching for what he's going through would be wonderful for your son to have in any case. This is something you might want to bring up with your primary physician. Many large medical operations have this sort of additional support services for their patients who are having chronic medical issues. I'm sure your doctor did not want your son to go through this sort of experience and will be willing any way they can to help in the future. Ask the doctor if the boy has to fast from all liquids before a blood draw in the future. The fainting and the difficult draws may be helped if he is able to drink water and stay hydrated before the blood draws. Getting that heart rate up may help too. Also, you could ask for a prescription of EMLA cream, which is a topical anesthetic salve which has saved me bunches of discomfort when I was having lots of blood drawn.
