Extreme weight loss
I know Jennifer lost most of that luscious baby fat by the mid-90s so she always looked different by the time movies like Dark City and Requiem for a Dream came out but seeing recent public pictures of her this year (2018) she looks really gaunt and depleted.
https://media.glamour.com/photos/56966040eaefd309768da9a8/master/w_1280,c_limit/fashion-2014-04-jennifer-connelly-nicolas-ghesquiere-louis-vuitton-dress-noah-premiere-main.jpg
https://1.bp.blogspot.com/-VkpiHV8Z0c0/WfPul5s4RSI/AAAAAAAADVg/P1q_nMacsAgjrF7qaamGHv0YHMMEJgZaQCLcBGAs/s1600/jennifer-connelly-volez-voguez-voyagez-louis-vuitton-exhibition-opening-in-nyc-3.jpg