Was that in doubles? As Dan_P mentioned, the weight of doubles ... you go from being able in an Al 80 to make depth adjustments with just breath control, etc., being able to whip around and check on your teammate--heck, do backflips if you want--to feeling like you're trying to turn an aircraft carrier. I agree with those who have said that doubles are actually more stable than a single tank in a certain sense--and that is when you're perfectly still and calm--but the air in the drysuit and the momentum of the tanks conspire to send you beyond the point of no return where you can no longer make corrections with breath alone. Then you're flailing around adding dumping adding dumping wing drysuit wing drysuit .... I have had multiple coaching sessions from multiple instructors on buoyancy control in the doubles and drysuit--and that's post-Drysuit and Doubles Primer--and it is still my nemesis. I suppose this is the result of having been SO accustomed to diving Al 80 and wetsuit.