medication and weight loss

Recently I have been light headed upon standing or even after I have been doing a physical activity and then stopping and standing still for a minute.  I have been taking 400 mg of sectral for almost a year to control svt.  Except for a brief episode of afib last spring I haven't had any problems until now.  I have lost about 35 pounds since January.(on a diet)  Would weight have anything to do with the amount of medicine I need to control the svt?  I was wondering if maybe I don't need as much sectral since I weigh less and the sectral is making my blood pressure drop too fast when I stand.  I was overweight before and needed to lose those pounds, and have not noticed a problem with the heart rate at these times, just light headed enough to sometimes have to sit down for a minute.  Do you think I need a medicine adjustment or is this something else?
Thank you for your response!
Cheryl

[Cleveland Clinic, MD]

It is possible that the dosage needs lowered although 400mg is not a hugh dose.  What is your heart rate?  Are you drinking enough fluids?  You could check with your doctor about cutting your dose down and see what he/she thinks.