I haven't had it but sometimes I do think that, and i don't want to sound mean, that it is jealousy. My bf's mum lost a lot of weight on sw and did get very slim, not unhealthily so but still very slim. Her mum, dad, sister etc were not happy for her, told her not to lose anymore, that she was too thin etc... They are all overweight themselves, have tried all the diets going for years etc but haven't succeeded and I feel that they are jealous of her - she has done something that they haven't been able to, and has kept it off because she has the motivation. I'm not saying that that's the case in your family at all but just an idea.
Also I think that when people lose a lot if weight, you really can see it in their face. And if your used to seeing so seeing someone with a bigger face it can be hard to get used to and they may look a bit gaunt for a while. It can take some adjusting to and others may worry that they have gone too far , are ill etc as a result.
