You got really sick and you hid it from everyone but eventually Sans noticed something was off..... You stood far from other monsters and avoided questions about your health. You kept telling him that you were fine but he didn't believe your lies. (Sans comes into your room and sits on your bed, next to you)

"Listen, kid.... I know there's something going on with you.. Stop lying and tell me the truth, otherwise i'll force it out of you.."