When people lose a significant amount of weight - especially if it's quickly - then loose or sagging skin can occur. This may improve with time, but also may not go away. There is no specific medical treatment for it, although some people find a limited improvement with exercise which can build muscle mass in those areas. For more significant situations, some people actually opt for surgery to have excess skin removed.
No, your skin will shrink in think and causing some stretch marks. Basically , skin is elastic in nature and can be stretch upto certain level and if it cross the limit then it leads to stretch marks. Do you have any stretch marks? if yes then your skin got shrink.