I had a friend who had the same problem. He actually overweighted himself but still could not get down. We finally figured out the problem was he wasn’t getting ALL the air out of his bcd. His inflator hose was velcroed down to minimize drag, but because it was velcroed down he was unable to dump all his air even though he thought he was. He didn’t want to keep undoing the velcro to get the entire hose straight up to dump, so he points himself head down and uses his dump valve. Me, I prefer to leave my inflator hose free so I can dump easily.