Some part of Jyn's mind realizes that Cassian is tugging at her hand but she's too warmly enveloped in sleep to be fully cognizant. Instead she murmurs "No" softly and draws her hand back.

Without letting go of his shirt.

Maybe she isn't completely aware or conscious, but Cassian is warm and she wants the warmth near her. "It's not morning, close your eyes." Or maybe she is completely aware and conscious and simply doesn't care.