Provided you have been through all the assessments, and do not smoke, the risk of surgery is minimal, particuarly since looking from your profile you are going to be operated on by a very eminent surgeon. Your ticker says you need to lose about 15 stone - is that right. If so, I think the risk of surgery is not as great as the risk of staying 15 stone overweight. Surgery is the very last resort and should not be considered until a person has tried all other methods, and if that person continually yo yoes with dieting and regaining, then many years can be wasted, with the toil on health, organs, joints etc. It is never too late to back out - even on the very morning of the op, if you have doubts. Although it is natural to have doubts, only you know what will happen if you do decide not to have surgery. Can you be absolutely sure you will be able to lose all that weight. You can be sure you will lose most or all of the excess weight if you have a bypass, which also incidentally may eliminate diabetes if you have it, or it will prevent you getting diabetes. Whatever happens, I wish you well.